Backup: Use new container names.

Docker Compose changed the name of the containers it creates.

crond/backup

@@ -11,7 +11,7 @@ set -eu
 # which should be a Docker volume.
 
 alias nc_run='docker exec -u www-data nextcloud-nextcloud-1'
-alias db_run='docker exec -u nobody nextcloud_mysql_1'
+alias db_run='docker exec -u nobody nextcloud-mysql-1'
 
 cleanup () {
     nc_run php occ maintenance:mode --off