Packing of BenchmarkDotNet.TestAdapter is broken

[AndreyAkinshin]

If we try to pack BenchmarkDotNet.TestAdapter, we will get the following error:

/Users/akinshin/Work/BenchmarkDotNet/.dotnet/sdk/8.0.100/Sdks/NuGet.Build.Tasks.Pack/buildCrossTargeting/NuGet.Build.Tasks.Pack.targets(221,5): error NU5129: Warning As Error: - At least one .props file was found in 'build/', but 'build/BenchmarkDotNet.TestAdapter.props' was not. [/Users/akinshin/Work/BenchmarkDotNet/src/BenchmarkDotNet.TestAdapter/BenchmarkDotNet.TestAdapter.csproj]
/Users/akinshin/Work/BenchmarkDotNet/.dotnet/sdk/8.0.100/Sdks/NuGet.Build.Tasks.Pack/buildCrossTargeting/NuGet.Build.Tasks.Pack.targets(221,5): error NU5129:  [/Users/akinshin/Work/BenchmarkDotNet/src/BenchmarkDotNet.TestAdapter/BenchmarkDotNet.TestAdapter.csproj]

It seems that it's caused by NuGet/Home#9055 Moving BenchmarkDotNet.TestAdapter.props from Package\ to build\ fixes the issue.

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A related problem is about our CI testing workflows. The BenchmarkDotNet.TestAdapter was introduced in #2438, but we failed to discover the problem it during the review process. Our automatic CI tests check the status of unit and integration tests, but they do not test that the solution can be packed. Meanwhile, merging non-packable projects to the master branch leads to a broken publish-nightly workflow.

We should introduce an additional workflow that checks the packability of the solution for the given PR.