sdk: Workload regression, installation fails for undefined platform alias

https://github.com/dotnet/sdk/pull/16956

And the associated design change say that a pack alias that is not defined for a given platform is not required. dotnet workload install microsoft-net-sdk-blazorwebassembly-aot has started failing on linux-x64 because there is no python pack defined for that platform.

Updated advertising manifest microsoft.net.workload.mono.toolchain.
Updated advertising manifest microsoft.net.sdk.android.
Updated advertising manifest microsoft.net.sdk.maccatalyst.
Updated advertising manifest microsoft.net.sdk.tvos.
Updated advertising manifest microsoft.net.sdk.ios.
Updated advertising manifest microsoft.net.sdk.macos.
Installing workload manifest microsoft.net.workload.mono.toolchain version 6.0.0-preview.6.21271.6.
[NuGet Manager] [Info]   GET https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   NotFound https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 83ms
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 87ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 81ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/6.0.0-preview.6.21271.6/microsoft.net.workload.mono.toolchain.manifest-6.0.100.6.0.0-preview.6.21271.6.nupkg
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/6.0.0-preview.6.21271.6/microsoft.net.workload.mono.toolchain.manifest-6.0.100.6.0.0-preview.6.21271.6.nupkg 215ms
Installing workload manifest microsoft.net.sdk.android version 30.0.100-ci.main.9.
[NuGet Manager] [Info]   GET https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   NotFound https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 57ms
[NuGet Manager] [Info]   NotFound https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 82ms
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 113ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/index.json 89ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/30.0.100-ci.main.9/microsoft.net.sdk.android.manifest-6.0.100.30.0.100-ci.main.9.nupkg
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/30.0.100-ci.main.9/microsoft.net.sdk.android.manifest-6.0.100.30.0.100-ci.main.9.nupkg 351ms
Workload installation failed, rolling back installed packs...
Installing workload manifest microsoft.net.workload.mono.toolchain version 6.0.0-preview.5.21270.12.
[NuGet Manager] [Info]   GET https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   NotFound https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 30ms
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 87ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/index.json 55ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/6.0.0-preview.5.21270.12/microsoft.net.workload.mono.toolchain.manifest-6.0.100.6.0.0-preview.5.21270.12.nupkg
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/flat2/microsoft.net.workload.mono.toolchain.manifest-6.0.100/6.0.0-preview.5.21270.12/microsoft.net.workload.mono.toolchain.manifest-6.0.100.6.0.0-preview.5.21270.12.nupkg 57ms
Installing workload manifest microsoft.net.sdk.android version 11.0.200-ci.main.256.
[NuGet Manager] [Info]   GET https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   NotFound https://api.nuget.org/v3/registration5-gz-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 30ms
[NuGet Manager] [Info]   NotFound https://pkgs.dev.azure.com/dnceng/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/825db618-e3eb-4426-ba54-b1d6e6c944d8/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 64ms
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/registrations2-semver2/microsoft.net.sdk.android.manifest-6.0.100/index.json 111ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/index.json
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/index.json 105ms
[NuGet Manager] [Info]   GET https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/11.0.200-ci.main.256/microsoft.net.sdk.android.manifest-6.0.100.11.0.200-ci.main.256.nupkg
[NuGet Manager] [Info]   OK https://pkgs.dev.azure.com/azure-public/3ccf6661-f8ce-4e8a-bb2e-eff943ddd3c7/_packaging/be90bfa8-5c00-452b-ba9f-226ce4366992/nuget/v3/flat2/microsoft.net.sdk.android.manifest-6.0.100/11.0.200-ci.main.256/microsoft.net.sdk.android.manifest-6.0.100.11.0.200-ci.main.256.nupkg 369ms
Workload installation failed: Duplicate workload manifest Microsoft.NET.Workload.Mono.ToolChain
install
  Install a workload.

Usage:
  dotnet [options] workload install [<PACKAGE_ID>...]

Arguments:
  <PACKAGE_ID>  The NuGet Package Id of the workload to install.

Options:
  --sdk-version <VERSION>                                                  The version of the SDK.
  --configfile <FILE>                                                      The NuGet configuration file to use.
  --add-source <SOURCE>                                                    Add an additional NuGet package source to use during installation.
  --skip-manifest-update                                                   Skip updating the workload manifests.
  --from-cache <from-cache>                                                Complete the operation from cache (offline).
  --download-to-cache <download-to-cache>                                  Download packages needed to install a workload to a folder which can be used for offline installation.
  --include-previews                                                       Allow prerelease workload manifests.
  --disable-parallel                                                       Prevent restoring multiple projects in parallel.
  --ignore-failed-sources                                                  Treat package source failures as warnings.
  --no-cache                                                               Do not cache packages and http requests.
  --interactive                                                            Allows the command to stop and wait for user input or action (for example to complete authentication).
  -v, --verbosity <d|detailed|diag|diagnostic|m|minimal|n|normal|q|quiet>  Set the MSBuild verbosity level. Allowed values are q[uiet], m[inimal], n[ormal], d[etailed], and diag[nostic].
  -?, -h, --help 

The failure is easy to reproduce by removing an alias for the platform you are testing on.

cc @mhutch @dsplaisted @mmitche @pranavkm