Merge pull request #3085 from overleaf/ho-mongo-4.0

bump mongo to 4.0.19 to see if tests pass on ci

GitOrigin-RevId: 70fa2ed6c33c4fa0f996fb975935b71e643fa1c7

services/web/docker-compose.ci.yml

@@ -61,4 +61,4 @@ services:
     image: redis
 
   mongo:
-    image: mongo:3.6.16
+    image: mongo:4.0.19

services/web/docker-compose.yml

@@ -66,4 +66,4 @@ services:
     image: redis
 
   mongo:
-    image: mongo:3.6.16
+    image: mongo:4.0.19