The recent PR #94868 has broken local running of libraries tests. After each test suite is completed, the following is printed to console and the test suite is reported as failed:

XUnitLogChecker.dll does not exist in the expected location: \XUnitLogChecker.dll

Looking at the eng/testing/RunnerTemplate.cmd, I can see that it builds the XUnitLogChecker.dll path like this:
set XUNITLOGCHECKER_DLL=%HELIX_CORRELATION_PAYLOAD%\XUnitLogChecker.dll
My guess is the problem is that the HELIX_CORRELATION_PAYLOAD is not set for local testing.