Update actions/upload-artifact action to v4

| datasource  | package                 | from | to |
| ----------- | ----------------------- | ---- | -- |
| github-tags | actions/upload-artifact | v2   | v4 |

Author: renovate[bot]

.github/workflows/forms-backend.yml

@@ -45,7 +45,7 @@ jobs:
       - name: Upload a Build Artifact
         if: always() && steps.prepare-artifact.outcome == 'success'
         continue-on-error: true
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: pull-request-payload
           path: pull_request_payload.json