[Flaky test] MultiThreadedArgument_BuildsProjectReferencesInProcess fails with MSB3883

## Description

`RunFileTests_BuildOptions.MultiThreadedArgument_BuildsProjectReferencesInProcess("0", "-mt")` intermittently fails on Linux x64 while building two project references in-process.

## Failure

```text
Microsoft.CSharp.Core.targets(97,5): error MSB3883: Unexpected exception:
error: Cannot release a lock that is not owned by the current thread.
```

The corresponding `("1", "-mt:false")` row passed.

## Evidence

- Failed in dotnet/sdk PR #56185, build `20260910.18`.
- Test history reports a 0.52% failure rate.
- Recent executions on both PR branches and `main` passed.
- All platform build legs passed.
- PR #56185 only changes Template Engine trie matching code and does not intersect this compiler path.

## Expected behavior

The multi-threaded build should complete reliably, or the underlying compiler/runtime lock-ownership race should be identified and isolated.

## Links

- PR: https://github.com/dotnet/sdk/pull/56185
- Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591121
- Helix log: https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-sdk-refs-pull-56185-merge-f93c200a568c4267b5/dotnet.Tests.dll.20/1/console.a04b3a4d.log?helixlogtype=result