Update Postgres image to 14.12

This is done to match the production version
which is used on AWS RDS, according to the most
recent maintenance by OPS in ticket OPS-10475.

tests/compose.yml

@@ -1,6 +1,6 @@
 services:
   db:
-    image: postgres:14.8-alpine3.18
+    image: postgres:14.12-alpine3.19
     container_name: hpc-postgres-test-api-core
     ports:
       - 6432:5432