ci: Cancel in-progress CI jobs when a PR is closed or merged (#5725)

* ci: Cancel in-progress CI jobs when a PR is closed or merged

The existing concurrency groups use `github.ref` which for PRs resolves
to `refs/pull/<number>/merge`. When a PR is merged, the push to main
creates a different concurrency group (`refs/heads/main`), so the
still-running PR workflows are never cancelled, wasting CI resources.

This adds a new workflow that triggers on `pull_request: closed` (fired
on both merge and manual close) and cancels all in-progress and queued
workflow runs for the PR's head branch via the GitHub API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(ci): Handle cancel errors gracefully in PR cleanup workflow

Wrap the cancelWorkflowRun call in try/catch so that if a run
completes between the list and cancel calls, the error doesn't
abort cancellation of the remaining runs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: antonis

.github/workflows/cancel-pr-workflows.yml

@@ -0,0 +1,51 @@
+name: Cancel PR Workflows
+
+on:
+  pull_request:
+    types: [closed]
+
+jobs:
+  cancel:
+    name: Cancel In-Progress Workflows
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel in-progress workflow runs
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { owner, repo } = context.repo;
+            const branch = context.payload.pull_request.head.ref;
+
+            const workflows = await github.rest.actions.listWorkflowRunsForRepo({
+              owner,
+              repo,
+              branch,
+              status: 'in_progress',
+            });
+
+            const waitingWorkflows = await github.rest.actions.listWorkflowRunsForRepo({
+              owner,
+              repo,
+              branch,
+              status: 'queued',
+            });
+
+            const runs = [...workflows.data.workflow_runs, ...waitingWorkflows.data.workflow_runs];
+
+            for (const run of runs) {
+              if (run.id === context.runId) {
+                continue;
+              }
+              try {
+                console.log(`Cancelling run ${run.id} (${run.name})`);
+                await github.rest.actions.cancelWorkflowRun({
+                  owner,
+                  repo,
+                  run_id: run.id,
+                });
+              } catch (error) {
+                console.log(`Failed to cancel run ${run.id}: ${error.message}`);
+              }
+            }
+
+            console.log(`Cancelled ${runs.length > 1 ? runs.length - 1 : 0} workflow run(s) for branch ${branch}`);