I’ve noticed the warning, that explains the issue
CSC : warning CS9057: The analyzer assembly '/home/runner/.nuget/packages/verify.mstest/28.2.0/analyzers/dotnet/roslyn4.4/cs/Verify.MSTest.SourceGenerator.dll' references version '4.9.0.0' of the compiler, which is newer than the currently running version '4.8.0.0'.
We will need to find, why the older version of Roslyn is called?