fix: ensure the latest postgres 17 container is pulled

So we have continuous feedback on any breakages in the Postgres 17
release series.

Author: auxesis

docker-compose.yml

@@ -1,6 +1,7 @@
 services:
   postgres: &postgres
     image: postgres:17
+    pull_policy: always
     container_name: postgres
     environment:
       PGPORT: 5432

tests/docker-compose.yml

@@ -1,6 +1,7 @@
 services:
   postgres: &postgres
     image: postgres:17
+    pull_policy: always
     container_name: postgres
     command: -c 'config_file=/etc/postgresql/postgresql.conf'
     restart: always