revert util.expand_path() due to regression

[Yobmod]

Hopefully to fix #1238.

The orginal change (commit 39eb0e6) was attempting to get mypy consistant with expand_path(None), as it doesn't like try except blocks without some type narrowing and expanduser doesn't accept None (triggering the Exception). Added mypy ignores for now, to allow CI to pass.

It passes tests either way, so can't be sure, but the traceback points to an overload of cmd.Git.excecute(), wherein cwd = self._working_dir.
That leads to Git.init(), where self._working_dir = expand_user(working_dir)

[Byron]

Thanks for the fix! What I understand is that the try-catch block has to be entered with None, which previously was prevented by the additional type check that mypi wanted to enforce.

It's quite amazing how GitPython seems to be at a state where minor changes will break someone, somewhere, under certain situations like multi-threading. It's a little frightening too.