👷 Add GitHub Action gate/check (#5492)

.github/workflows/test.yml

@@ -75,3 +75,19 @@ jobs:
         with:
           name: coverage-html
           path: htmlcov
+
+  # https://github.com/marketplace/actions/alls-green#why
+  check:  # This job does nothing and is only used for the branch protection
+
+    if: always()
+
+    needs:
+      - coverage-combine
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Decide whether the needed jobs succeeded or failed
+        uses: re-actors/alls-green@release/v1
+        with:
+          jobs: ${{ toJSON(needs) }}