Switch CI to merge queues

.github/workflows/ci.yml

@@ -1,11 +1,7 @@
 name: CI
 
 on:
-  push:
-    # Run in PRs and for bors, but not on master.
-    branches:
-      - 'auto'
-      - 'try'
+  merge_group:
   pull_request:
     branches:
       - 'master'
@@ -68,27 +64,24 @@ jobs:
       - name: rustdoc
         run: RUSTDOCFLAGS="-Dwarnings" ./miri doc --document-private-items
 
-  # These jobs doesn't actually test anything, but they're only used to tell
-  # bors the build completed, as there is no practical way to detect when a
-  # workflow is successful listening to webhooks only.
-  #
-  # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
-  end-success:
-    name: bors build finished
-    runs-on: ubuntu-latest
+  conclusion:
     needs: [build, style]
-    if: github.event.pusher.name == 'bors' && success()
-    steps:
-      - name: mark the job as a success
-        run: exit 0
-  end-failure:
-    name: bors build finished
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    #
+    # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+    if: ${{ !cancelled() }}
     runs-on: ubuntu-latest
-    needs: [build, style]
-    if: github.event.pusher.name == 'bors' && (failure() || cancelled())
     steps:
-      - name: mark the job as a failure
-        run: exit 1
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+            # Print the dependent jobs to see them in the CI log
+            jq -C <<< '${{ toJson(needs) }}'
+            # Check if all jobs that we depend on (in the needs array) were successful.
+            jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'
 
   cron-fail-notify:
     name: cronjob failure notification