`Requires=` has the behaviour of stopping `gitea.service` when the
database is stopped but not bringing it up again after the database is
started again. Use `Wants=` to define a weak requirement instead,
meaning `gitea.service` will be kept running when the database is
stopped, which is not an issue because gitea will just reconnect later
on.
Fixes: https://github.com/go-gitea/gitea/issues/15866
Co-authored-by: zeripath <art27@cantab.net>