Change CI docker image to use postgis docker image for the DB

docker-compose.yml

@@ -5,7 +5,7 @@ services:
       - "6379:6379"
 
   db:
-    image: postgres:14-alpine
+    image: postgis/postgis:14-3.5-alpine
     # To preserve data between runs of docker compose, we mount a folder from the host machine.
     volumes:
       - dbdata:/var/lib/postgresql/data