Changes

jobs/test-override: run `cosa fetch` with `--with-cosa-overrides`

Otherwise, if the override we're testing is pulling in new
dependencies, we won't know to fetch them. This came up in
https://bodhi.fedoraproject.org/updates/FEDORA-2024-969f546f80 which is
adding a dep on `composefs`.

This also matches CI in the coreos/fedora-coreos-config repo.

(Aside: we've talked in the past about getting notified when new deps
are added and the previous behaviour coincidentally did that, but this
doesn't seem like the right place for it; we shouldn't block packages
from entering Fedora on that account. That check probably belongs in
`bump-lockfile` instead).