Update more tests not to use Python 3.8
Update a few more tests to avoid using Python 3.8 unnecessarily.
From what I can see, neither of these really need that specific Python
version, so just update them to use 3.9 instead.
Bug #13676
avoid fetching an exact, cached commit, even if it isn't locked
This is a rough draft of one approach we might take to fixing
https://github.com/astral-sh/uv/issues/13513