Add conclusion job to PR CI

.github/workflows/clippy_pr.yml

@@ -62,3 +62,24 @@ jobs:
       run: .github/driver.sh
       env:
         OS: ${{ runner.os }}
+
+  # We need to have the "conclusion" job also on PR CI, to make it possible
+  # to add PRs to a merge queue.
+  conclusion:
+    needs: [ base ]
+    # 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: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'