test/test_zzz_keys.py: move from test/test_keys.py

Rename the file so it runs last, as it's currently failing a lot of
times on sourcehut. When I looked into it last time, it seemed to be
related to CDN caching and then it worked again so I didn't look further
into it at the time. Move it to the end until this is figured out
properly, so at least we see if all other tests are passing.

test/test_zzz_keys.py

@@ -1,5 +1,7 @@
 # Copyright 2023 Oliver Smith
 # SPDX-License-Identifier: GPL-3.0-or-later
+# This file has a _zzz_ prefix so it runs last, because it tends to fail on
+# sourcehut currently. Related to some CDN caching issue probably.
 import os
 import sys
 import pytest