Update dev-backend-docker-compose.yml

Co-authored-by: Andrew Ferrazzutti <andrewf@element.io>

dev-backend-docker-compose.yml

@@ -63,8 +63,8 @@ services:
       - UID=0
       - GID=0
     volumes:
-      - ./backend/synapse_tmp:/data
+      - ./backend/synapse_tmp:/data:Z
-      - ./backend/dev_homeserver.yaml:/data/cfg/homeserver.yaml
+      - ./backend/dev_homeserver.yaml:/data/cfg/homeserver.yaml:Z
     networks:
       - ecbackend