fix calculation for the labels to apply (#294)

fix calculation for the labels to apply
diff --git a/pkgs/sdk_triage_bot/lib/triage.dart b/pkgs/sdk_triage_bot/lib/triage.dart
index 9529e98..d5c1fb7 100644
--- a/pkgs/sdk_triage_bot/lib/triage.dart
+++ b/pkgs/sdk_triage_bot/lib/triage.dart
@@ -124,7 +124,7 @@
   await githubService.createComment(sdkSlug, issueNumber, comment);
 
   final allRepoLabels = (await githubService.getAllLabels(sdkSlug)).toSet();
-  final labelAdditions = newLabels.toSet().union(allRepoLabels).toList()
+  final labelAdditions = newLabels.toSet().intersection(allRepoLabels).toList()
     ..sort();
   if (labelAdditions.isNotEmpty) {
     labelAdditions.add('triage-automation');