Cancel in progress actions for PRs on subsequent pushes

https://docs.github.com/en/enterprise-cloud@latest/actions/writing-workflows/choosing-what-your-workflow-does/control-the-concurrency-of-workflows-and-jobs

.github/workflows/ci.yml

@@ -19,6 +19,13 @@ on:
     branches:
       - "main"
 
+concurrency:
+  # Use github.run_id on main branch
+  # Use github.event.pull_request.number on pull requests, so it's unique per pull request
+  # Use github.ref on other branches, so it's unique per branch
+  group: ${{ github.workflow }}-${{ github.ref == 'refs/heads/main' && github.run_id || github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 env:
   GITHUB_TOKEN: ${{ secrets.PULUMI_BOT_TOKEN }}
   PULUMI_ACCESS_TOKEN: ${{ secrets.PULUMI_ACCESS_TOKEN }} # Used by test-containers.sh\