Use Wants= over Requires= in systemd file (#15897)

`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: #15866

Co-authored-by: zeripath <art27@cantab.net>

Author: silverwind

contrib/systemd/gitea.service

@@ -3,22 +3,22 @@ Description=Gitea (Git with a cup of tea)
 After=syslog.target
 After=network.target
 ###
-# Don't forget to add the database service requirements
+# Don't forget to add the database service dependencies
 ###
 #
-#Requires=mysql.service
+#Wants=mysql.service
 #After=mysql.service
 #
-#Requires=mariadb.service
+#Wants=mariadb.service
 #After=mariadb.service
 #
-#Requires=postgresql.service
+#Wants=postgresql.service
 #After=postgresql.service
 #
-#Requires=memcached.service
+#Wants=memcached.service
 #After=memcached.service
 #
-#Requires=redis.service
+#Wants=redis.service
 #After=redis.service
 #
 ###