Local build failing when trying to access VS extension testing nuspec file

[RikkiGibson]

2 mornings in a row I have logged in, checked out a commit, run .\Build.cmd -restore, and gotten the following result:

​Build FAILED.

C:\Program Files\dotnet\sdk\10.0.100\NuGet.Build.Tasks.Pack.targets(222,5): error : The process cannot access the file
'F:\src\roslyn\artifacts\obj\Microsoft.VisualStudio.Extensibility.Testing.SourceGenerator\Debug\Microsoft.VisualStudio.
Extensibility.Testing.SourceGenerator.5.3.0-dev.nuspec' because it is being used by another process. [F:\src\roslyn\src
\VisualStudio\IntegrationTest\Harness\SourceGenerator\Microsoft.VisualStudio.Extensibility.Testing.SourceGenerator.cspr
oj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:04:20.25
Build failed with exit code 1. Check errors above.

When I get this result, then run the exact same command again, I get a successful build.

@dibarbet for visibility

[jjonescz]

This can be seen in CI too - e.g., https://github.com/dotnet/roslyn/pull/81900/checks?check_run_id=59671054826

[jjonescz]

@dbreshears as box lead to triage