If the gitea service is stopped because of the db going down
it needs an `After=db.service` to ensure it is restarted in
addition to the `Requires=db.service` to ensure that the db
is started before gitea is started.
Fix#15866
An error occurred
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>