Update startup-tests.yml

avoid using a secret for postres password:
- this has no security benefit, as the service is running on localhost for the test runner
- this makes external PRs fail, because they are not allowed to get the secret.
To be reviewed before merge.

.github/workflows/startup-tests.yml

@@ -18,7 +18,7 @@ jobs:
         image: postgres:14.1
         env:
           POSTGRES_USER: postgres
-          POSTGRES_PASSWORD: ${{ secrets.POSTGRES_PASSWORD }}
+          POSTGRES_PASSWORD: postgres
           POSTGRES_DB: postgres
         ports: ["5432:5432"]
         options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5