Update docker.io/library/postgres Docker tag to v18

docker-compose.yml

@@ -95,7 +95,7 @@ services:
       - ldap_api_key
 
   db_pg17:
-    image: docker.io/library/postgres:17.11
+    image: docker.io/library/postgres:18.6
     container_name: authentik_db_pg17
     restart: unless-stopped
     healthcheck: