[MM] Bump to 7.9.1

mattermost/docker-compose.yml

@@ -11,11 +11,11 @@ services:
     env_file: secrets/db.secrets
 
   app:
-    image: mm_app:7.7.1
+    image: mm_app:7.9.1
     build:
       context: .
       args:
-        MM_VERSION: 7.7.1
+        MM_VERSION: 7.9.1
     depends_on:
       - db
     restart: unless-stopped