genosxversion: don't give up if we can't find a path to hg libraries
This doesn't work if you have a PyOxidized hg on $PATH, but everything
is fine if you just ignore that problem.
Differential Revision: https://phab.mercurial-scm.org/D8975
Manuel Jacob <me@manueljacob.de> [Wed, 02 Sep 2020 01:30:56 +0200] rev 45396
tests: fix test-demandimport.py on Python 3.9
Starting with Python 3.9, importing importlib.resources (indirectly) imports
the zipfile module. Therefore, the module is not suitable for the test.
Instead, we can use the ftplib module, which is very unlikely to be imported
during the test run.