fix(ci): safely sync issue metadata to PR without overwriting labels

- Replaced `setLabels()` with `addLabels()` to prevent race conditions
  where concurrent label additions could be lost.
- Labels from linked issues are now added without removing existing PR labels.
- Milestones from linked issues continue to be synced.
- Adds a comment to the PR summarizing synchronized metadata.

Author: sheikhlimon

.github/workflows/autolabel-pr-issue.yml

@@ -47,7 +47,7 @@ jobs:
             core.setOutput('issues', JSON.stringify(Array.from(issueNumbers)));
             core.setOutput('pr', prNumber.toString());
 
-      # Step 3: Sync issue metadata to PR
+      # Step 3: Sync issue metadata to PR safely
       - name: Sync Issue Metadata to PR
         if: steps.extract-issues.outputs.issues != '' && steps.extract-issues.outputs.issues != '[]'
         uses: actions/github-script@v7
@@ -80,24 +80,16 @@ jobs:
 
                 console.log(`Syncing metadata from Issue #${issueNumber} to PR #${prNumber}`);
 
-                // --- Sync Labels ---
+                // --- Sync Labels safely using addLabels ---
                 const issueLabels = issue.labels.map(l => l.name);
-                const { data: pr } = await github.rest.pulls.get({
-                  owner: context.repo.owner,
-                  repo: context.repo.repo,
-                  pull_number: prNumber
-                });
-                const currentPRLabels = pr.labels.map(l => l.name);
-                const combinedLabels = Array.from(new Set([...currentPRLabels, ...issueLabels]));
-
-                if (combinedLabels.length > 0) {
-                  await github.rest.issues.setLabels({
+                if (issueLabels.length > 0) {
+                  await github.rest.issues.addLabels({
                     owner: context.repo.owner,
                     repo: context.repo.repo,
                     issue_number: prNumber,
-                    labels: combinedLabels
+                    labels: issueLabels
                   });
-                  console.log(`Labels applied: ${combinedLabels.join(', ')}`);
+                  console.log(`Labels added from issue: ${issueLabels.join(', ')}`);
                 }
 
                 // --- Sync Milestone ---
@@ -111,7 +103,7 @@ jobs:
                   console.log(`Milestone synced: ${issue.milestone.title}`);
                 }
 
-                // --- Optionally add comment on PR ---
+                // --- Add comment on PR ---
                 await github.rest.issues.createComment({
                   owner: context.repo.owner,
                   repo: context.repo.repo,