arcade: restore.sh fails on arm64 Macs

1. Use macOS on an arm64 device.
2. Uninstall any system .NET SDKs.
3. Run ./restore.sh from a clean Roslyn checkout.

Not sure whether this is a bug in Roslyn’s build scripts, Arcade, or dotnet-install. It is trying to install the 3.1.0 runtime, which is fine, but it is trying to find an arm64 version, which has never existed (macOS arm64 support was added in .NET 5). This should be installing the x64 3.1.0 runtime instead.

dotnet-install: Note that the intended use of this script is for Continuous Integration (CI) scenarios, where:
dotnet-install: - The SDK needs to be installed without user interaction and without admin rights.
dotnet-install: - The SDK installation doesn't need to persist across multiple CI runs.
dotnet-install: To set up a development environment or to run apps, use installers rather than this script. Visit https://dotnet.microsoft.com/download to get the installer.

dotnet-install: Attempting to download using primary link https://dotnetcli.azureedge.net/dotnet/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at primary link 'https://dotnetcli.azureedge.net/dotnet/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz' is not available.
dotnet-install: Attempting to download using legacy link https://dotnetcli.azureedge.net/dotnet/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at legacy link 'https://dotnetcli.azureedge.net/dotnet/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz' is not available.
dotnet-install: Attempting to download using primary link https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at primary link 'https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz' is not available.
dotnet-install: Attempting to download using legacy link https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at legacy link 'https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz' is not available.
dotnet_install: Error: Could not find `.NET Core Runtime` with version = 3.1.0
dotnet_install: Error: Refer to: https://aka.ms/dotnet-os-lifecycle for information on .NET Core support
Failed to install dotnet from public_location.
Attempting to install dotnet from dotnetbuilds.
dotnet-install: Note that the intended use of this script is for Continuous Integration (CI) scenarios, where:
dotnet-install: - The SDK needs to be installed without user interaction and without admin rights.
dotnet-install: - The SDK installation doesn't need to persist across multiple CI runs.
dotnet-install: To set up a development environment or to run apps, use installers rather than this script. Visit https://dotnet.microsoft.com/download to get the installer.

dotnet-install: Attempting to download using primary link https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at primary link 'https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-runtime-3.1.0-osx-arm64.tar.gz' is not available.
dotnet-install: Attempting to download using legacy link https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz
curl: (22) The requested URL returned error: 404
dotnet-install: The resource at legacy link 'https://dotnetbuilds.azureedge.net/public/Runtime/3.1.0/dotnet-osx-arm64.3.1.0.tar.gz' is not available.
dotnet_install: Error: Could not find `.NET Core Runtime` with version = 3.1.0
dotnet_install: Error: Refer to: https://aka.ms/dotnet-os-lifecycle for information on .NET Core support
Failed to install dotnet from dotnetbuilds.
Failed to install dotnet SDK from any of the specified locations.
/Users/sandy/.nuget/packages/microsoft.dotnet.arcade.sdk/7.0.0-beta.22411.2/tools/InstallDotNetCore.targets(15,5): error : dotnet-install failed [/Users/sandy/.nuget/packages/microsoft.dotnet.arcade.sdk/7.0.0-beta.22411.2/tools/Tools.proj]

Build FAILED.

/Users/sandy/.nuget/packages/microsoft.dotnet.arcade.sdk/7.0.0-beta.22411.2/tools/InstallDotNetCore.targets(15,5): error : dotnet-install failed [/Users/sandy/.nuget/packages/microsoft.dotnet.arcade.sdk/7.0.0-beta.22411.2/tools/Tools.proj]
    0 Warning(s)
    1 Error(s)