Group test results in a single downstream job (#4078)

## Why

We need a single "required check" for tests. Now that we split tests
into separate jobs that may or may not be skipped, they can no longer be
required checks themselves. This new downstream job that groups the
result of all of them will always run and can become the new "required
check".

Author: pietern

.github/workflows/push.yml

@@ -270,6 +270,23 @@ jobs:
         run: |
           make test-pipelines
 
+  # This job groups the result of all the above test jobs.
+  # If any of them failed, this job will be skipped.
+  # It is a required check, so it blocks auto-merge and the merge queue.
+  test-result:
+    needs:
+      - test
+      - test-exp-aitools
+      - test-exp-apps-mcp
+      - test-exp-ssh
+      - test-pipelines
+
+    name: test-result
+    runs-on: ubuntu-latest
+
+    steps:
+      - run: echo "All tests passed ✅"
+
   validate-generated-is-up-to-date:
     needs: cleanups
     runs-on: ubuntu-latest