fix(test): Remove locking and fix prometheus test

All tests within a file run in the same worker and out test DB names are unique per file as well.
We don't really need a locking mechanism here.

Same is valid for the test-emails. The only potential issue is that it might try to create the test-emails dir multiple times (at the very same time) and thus run into an error. However, that can be covered by specifying exist_ok=True with os.makedirs such that those errors are ignored.

Signed-off-by: moson moson@archlinux.org