Update GitHub Actions workflow to use new S3 URL for Postgres SSL certificate

- Changed the S3 URL variable for downloading the Postgres SSL certificate in the GitHub Actions workflow from `PG_CERT_S3_URL` to `CERT_S3_URL`.
- This update ensures the workflow correctly references the updated secret for SSL certificate retrieval, improving the reliability of the deployment process.

.github/workflows/porter_app_staging_3155.yml

@@ -37,7 +37,7 @@ jobs:
       - name: Download Postgres certificate from S3
         run: |
           mkdir -p ~/.postgresql
-          aws s3 cp ${{ secrets.PG_CERT_S3_URL }} ~/.postgresql/root.crt
+          aws s3 cp ${{ secrets.CERT_S3_URL }} ~/.postgresql/root.crt
 
       - name: Run migrations
         run: diesel migration run