chore(dev): Use postgres:15 for docker-compose.yml (#8029)

This will ensure we're using the latest Postgres major, which should
more closely track staging/prod.

docker-compose.yml

@@ -1,7 +1,7 @@
 services:
   # Dependencies
   postgres:
-    image: postgres:15.5
+    image: postgres:15
     volumes:
       - postgres-data:/var/lib/postgresql/data
     environment: