Upgrade Gitea's backend DB to MariaDB 10.11

After upgrading MariaDB behind several services from 10.4 to 10.11 it is
now Gitea's turn. Use the auto upgrade method as we've done elsewhere
and update Gitea's DB too.

Change-Id: I01aab3c55f1af4f883efe05bf8862ccd50a07631

playbooks/roles/gitea/templates/docker-compose.yaml.j2

@@ -4,7 +4,7 @@ version: '2'
 
 services:
   mariadb:
-    image: docker.io/library/mariadb:10.4
+    image: docker.io/library/mariadb:10.11
     network_mode: host
     restart: always
     environment:
@@ -12,6 +12,7 @@ services:
       MYSQL_DATABASE: gitea
       MYSQL_USER: "{{ gitea_db_username }}"
       MYSQL_PASSWORD: "{{ gitea_db_password }}"
+      MARIADB_AUTO_UPGRADE: 1
     volumes:
       - /var/gitea/db:/var/lib/mysql
       - /var/gitea/conf/99-max_conn_my.cnf:/etc/mysql/conf.d/99-max_conn_my.cnf:ro