run-tests: avoid os.getcwdb() on Windows
Any call to this issues a DeprecationWarning about the Windows bytes API being
deprecated. There are a handful of these calls in core, but test-run-tests.t
was littered with these, as it's printed everytime run-tests.py is launched.
I'm not sure what the long term strategy for Unicode on Windows in the test
runner is, but this seems no worse than the current conversion strategy.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).