Update actions/download-artifact action to v4

Author: renovate[bot]

.github/workflows/verify.yml

@@ -333,7 +333,7 @@ jobs:
           echo "Failed to restore Python virtual environment from cache"
           exit 1
       - name: Download all coverage artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
       - name: Combine coverage results
         run: |
           . venv/bin/activate