mypy's move to external types-* packages is a PITA, as it requires them
to be installed in site-packages, and provides no way to specify a custom
site-packages folder, necessitating extra scripts to mock the
site-packages path, and copy+rename the stub packages into a separate
folder.
https://github.com/ankitects/anki/pull/889
- We can't use compare_locales's getChecker(), as it seems to
be focused on checking translations rather than the original
templates.
- Also fix return code not being passed on in check_files()
- Temporarily pin pip-tools, as its output format has changed
