Investigate test failures with "An operation is not legal in the current state."

[wtgodbe]

Starting with #14425, we've been seeing lots of test failures of the following type:

System.IO.FileLoadException : Could not load file or assembly 'Microsoft.Net.Http.Headers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. An operation is not legal in the current state. (0x80131509)

We think this is related to the large number of Explicit references that we've added to the tests. We should investigate these failures as they may represent an issue with the runtime.

CC @aspnet/build @mmitche

[dougbu]

Would like to first determine whether this is about flakiness in our eng\targets\ResolveReferences.targets versus in the .NET SDK. To that end, the initial task here might be to create a project with lots and lots of explicit <ProjectReference>s and <PackageReference>s but none of the AspNetCore <Reference> infrastructure, then build it over and over.

[mkArtakMSFT]

@wtgodbe this should move to a proper milestone. I think this milestone is already locked down, so we should close it.

[wtgodbe]

We think this will be fixed by #17311 - if so I'll close when that's merged

[dougbu]

Close once merge into 'release/3.1' is done

[wtgodbe]

We stopped seeing these after #17311, closing