Fix debug trace test

[Steve Lee (SteveL-MSFT)]

PR Summary

The PSAdapter Write-Debug test fails inconsistently on macOS. macOS is known to not flush stdio buffers when a process exits so there's a race condition where the pwsh process has exited before the debug trace was written to stderr. The timing of this seems to be due to the Write-Error in the test class that follows Write-Debug. Due to PSAdapter setting $ErrorActionPreference = 'stop' the Write-Error results in an exception that is caught and exits the adapter before the debug message is written out.

Two changes:

• In the PSAdapter, write the trace queue before writing the exception. This shouldn't affect this problem, but this order is correct
• In the test class, explicitly set $ErrorActionPreference = 'continue' since the test is only trying to write an error trace and not throw an exception