Update postgres Docker tag to v18

.github/workflows/python-app.yml

@@ -12,7 +12,7 @@ jobs:
 
     services:
       database:
-        image: postgres:17-alpine
+        image: postgres:18-alpine
         env:
           # password for postgres user in the Docker container
           POSTGRES_PASSWORD: postgres
@@ -27,7 +27,7 @@ jobs:
           - 5432:5432
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v5
     - name: Install uv
       uses: astral-sh/setup-uv@v7
       with: