Add labeled and unlabeled events for PR changelog check action.

Signed-off-by: Xun Jiang <jxun@vmware.com>

.github/workflows/pr-changelog-check.yml

@@ -1,5 +1,9 @@
 name: Pull Request Changelog Check
-on: [pull_request]
+# by setting `on: [pull_request]`, that means action will be trigger when PR is opened, synchronize, reopened.
+# Add labeled and unlabeled events too.
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, labeled, unlabeled]
 jobs:
 
   build:

changelogs/unreleased/5157-jxun

@@ -0,0 +1 @@
+Add labeled and unlabeled events for PR changelog check action.