chore: update changeset job to work with merge queues

The merge group event is triggered on a group of PRs, so the existing
approach would fail on looking up the PR number.

The job now splits into the merge group context and the single pr
context. In the Merge group context, the same check as the single pr
approach is applied to each of the PRs in the merge group.

Author: kanej

.github/workflows/check-changeset-added.yml

@@ -26,6 +26,67 @@ jobs:
       - uses: actions/github-script@v7
         with:
           script: |
+            const isMergeGroup = context.eventName === "merge_group";
+
+            // Merge group context
+            if (isMergeGroup) {
+              console.log("Running in merge_group context...");
+              const { data: mergeQueue } = await github.rest.repos.listPullRequestsAssociatedWithCommit({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                commit_sha: context.sha
+              });
+
+              if (mergeQueue.length === 0) {
+                console.log("No associated PRs found for this merge_group commit.");
+                process.exit(1);
+              }
+
+              console.log(`Found ${mergeQueue.length} PR(s) in the merge group.`);
+
+              for (const pr of mergeQueue) {
+                const pullNumber = context.issue.number;
+
+                console.log(`Checking PR #${pr.number}...`);
+                const { data: files } = await github.rest.pulls.listFiles({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  pull_number: pullNumber
+                });
+
+                const changeset = files.find(
+                  file => file.status === "added" && file.filename.startsWith(".changeset/")
+                );
+
+                if (changeset !== undefined) {
+                  console.log(`PR #${pr.number} has a changeset: ${changeset.filename}`);
+                  continue;
+                }
+
+                console.log(`PR #${pr.number} has no changeset.`);
+
+                const { data: prDetails } = await github.rest.pulls.get({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  pull_number: pullNumber
+                });
+
+                const noChangesetNeededLabel = prDetails.labels.some(l => l.name === "no changeset needed");
+
+                if (noChangesetNeededLabel) {
+                  console.log(`PR #${pr.number} is labeled as "no changeset needed".`);
+                  continue;
+                }
+
+                console.log(`PR #${pr.number} is not labeled as "no changeset needed". Failing job.`);
+                process.exit(1);
+              }
+
+              console.log("All PRs in the merge group have a changeset or are labeled correctly.");
+              return;
+            }
+
+            // Single PR context
             const pullNumber = context.issue.number;
 
             const { data: files } = await github.rest.pulls.listFiles({