feat: provide stable-named job for branch protection (#124)

* feat: provide stable-named job for branch protection

GitHub actions matrix "test" gets expanded to many status checks, making it impossible to keep the branch protection settings in the GitHub UI up-to-date as the matrix cells are updated.

This provides a "conclusion" status which can be used instead. Thanks @mattmoor for the code!

* Update ci.yaml

.github/workflows/ci.yaml

@@ -29,3 +29,23 @@ jobs:
         [
           {"folder": ".", "bzlmodEnabled": false}
         ]
+  # For branch protection settings, this job provides a "stable" name that can be used to gate PR merges
+  # on "all matrix jobs were successful".
+  conclusion:
+    needs: test
+    runs-on: ubuntu-latest
+    if: always()
+    steps:
+      - uses: technote-space/workflow-conclusion-action@45ce8e0eb155657ab8ccf346ade734257fd196a5 # v3.0.3
+
+      # Note: possible conclusion values:
+      # https://github.com/technote-space/workflow-conclusion-action/blob/main/src/constant.ts
+      - name: report success
+        if: ${{ env.WORKFLOW_CONCLUSION == 'success' }}
+        working-directory: /tmp
+        run: echo ${{ env.WORKFLOW_CONCLUSION }} && exit 0
+
+      - name: report failure
+        if: ${{ env.WORKFLOW_CONCLUSION == 'failure' }}
+        working-directory: /tmp
+        run: echo ${{ env.WORKFLOW_CONCLUSION }} && exit 1