Define all_required_checks task as the convenient waiting point (#813)

`update_coverage` action used to wait for `validate_asciidoc` to succeed as the task that takes the longest. After #782 is merged as f21f23b9860c10d4effb00b6022917bc28e02e61 it is no longer the case. This change introduces `all_required_checks` task that depends on all checks required for a PR to be merged, thus providing a single point that is known to succeed last and can be safely waited upon.

.cirrus.yml

@@ -106,3 +106,17 @@ validate_links_task:
     - ./ci/validate_links.sh ${LINK_CACHE_PATH}
     - bash ci/cirrus-cache.sh upload ${LINK_CACHE_NAME} ${LINK_CACHE_PATH}
 
+all_required_checks_task:
+  depends_on:
+    - tooling_tests
+    - frontend_tests
+    - validate_metadata
+    - validate_asciidoc
+  gke_container:
+    <<: *CONTAINER_DEFINITION
+    dockerfile: ci/Dockerfile
+    cpu: 1
+    memory: 1G
+  print_message_script:
+    - echo 'All required checks have passed'
+

.github/workflows/update_coverage.yml

@@ -63,7 +63,7 @@ jobs:
       id: wait-for-build
       with:
         token: ${{ secrets.GITHUB_TOKEN }}
-        checkName: validate_asciidoc # usually the longest task
+        checkName: all_required_checks
         ref: ${{ env.TMP_BRANCH }}
         timeoutSeconds: 2400
         intervalSeconds: 30