chore: add unlabeled trigger to changelog-preview (#1189)

Author: BYK

.github/workflows/changelog-preview.yml

@@ -2,7 +2,7 @@
 name: Changelog Preview
 on:
   pull_request_target:
-    types: [opened, synchronize, reopened, edited, labeled]
+    types: [opened, synchronize, reopened, edited, labeled, unlabeled]
 
 permissions:
   contents: read