aspnetcore: [.NET 6] [Source Compat Failure] NSK app doesn't publish with .net6.0 SDK

Application Name: NSK OS: Windows 10 RS5 CPU: X64 .NET Build Number: 6.0.100-preview.1.21071.10 Project Location: https://github.com/andysal/NSK

Verify Scenarios: 1). Windows 10 RS5 X64 + .NET Core SDK build 6.0.100-preview.1.21071.10: Fail 2). Windows 10 RS5 X64 + .NET Core SDK build 5.0.102: Pass

Repro steps

1. Source Code check at https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1268776
2. dotnet publish Nsk.Web.Site.sln

Expected Result: Build succeeded

Actual Result:

C:\Program Files\dotnet\sdk\6.0.100-preview.1.21071.10\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.ConflictResolution.targets(108,5): error NETSDK1148: Found multiple publish output files with the same relative path: C:\Users\valtunc\Desktop\AppSources\NSK\netcore\src\Nsk.Web.Site.Areas.Admin\libman.json, C:\Users\valtunc\Desktop\AppSources\NSK\netcore\src\Nsk.Web.Site\libman.json. [C:\Users\valtunc\Desktop\AppSources\NSK\netcore\src\Nsk.Web.Site\Nsk.Web.Site.csproj]

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