git: update check for invalid URL characters to work with Python versions that include an attempt at fixing the very same problem

With changes like
https://github.com/python/cpython/commit/76cd81d60310d65d01f9d7b48a8985d8ab89c8b4
making it to Python 3.10 and being backported to previous Python versions, the
approach in a8a51a3bdb61 no longer works when combined with
urllib.parse.urlparse in d2f59de17bef: path will never contain the invalid
characters.

To catch this case anyway, add a new check to verify that the parsed URL can
roundtrip back to the original representation with urllib.parse.urlunparse .

The actual exception might vary, but one of them should always fire.

There is a risk that the new check will reject some URLs that somehow isn't
normalized. No such cases have been found yet.