[web] use a tmpfs for the data-dir of the acceptance tests (#23571)

Moving mongodb onto a tmpfs requires too much memory.

GitOrigin-RevId: e870ed8b5349c13e948f7037369fb52356cd562c

services/web/docker-compose.ci.yml

@@ -45,6 +45,8 @@ services:
       - mongo
       - saml
       - ldap
+    tmpfs:
+      - /overleaf/services/web/data
 
   test_frontend:
     build: