drsyms fails to query file-private C++ symbols in GA CI windows-2019 VS2019 drsyms-test

Splitting from #5195 (closed). Our drsyms-test has failed ever since we went to the Github Actions windows-2019 platform using VS2019. See some analysis of which dbghelp is being used here: https://github.com/DynamoRIO/dynamorio/issues/5195#issuecomment-1064668457

Locally on my win10-21H1 machine I can't reproduce the failure: I have VS2019 and I tried with both the dbghelp.dll that comes with a full VS2019 install and I tried with the Windows Kit 10 one which should match what GA CI is using.

We've had some trouble with tmate recently. This would be easiest to figure out if someone could reproduce it locally.