Merge pull request #8390 from overleaf/msm-update-ce-mongo-4_2

[CE] Update mongo to 4.2 in legacy `docker-compose.yml`

GitOrigin-RevId: 86894db55a52dd60b17102fb698f6443a3b980af

docker-compose.yml

@@ -103,7 +103,7 @@ services:
 
     mongo:
         restart: always
-        image: mongo:4.0
+        image: mongo:4.2
         container_name: mongo
         expose:
             - 27017