ci: pin postgres version to 15

tools/compose/traefik-secure.yml

@@ -8,7 +8,7 @@ version: "3.8"
 services:
   # Database (Postgres)
   postgres:
-    image: postgres:alpine
+    image: postgres:15-alpine
     restart: unless-stopped
     volumes:
       - postgres_data:/var/lib/postgresql/data