Add CHANGELOG.md modification check and warning comment

.github/workflows/pr-checks.yml

@@ -181,6 +181,31 @@ jobs:
           path: ${{ runner.temp }}/repo-size/
           if-no-files-found: error
 
+      - name: Check for CHANGELOG.md changes
+        id: changelog-check
+        if: steps.fetch-base.outcome == 'success'
+        env:
+          BASE_SHA: ${{ steps.fetch-base.outputs.merge_base }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          if ! git diff --exit-code --quiet "$BASE_SHA" "$HEAD_SHA" -- CHANGELOG.md; then
+            echo "CHANGELOG.md was modified in this PR."
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Post a warning about modifying CHANGELOG.md
+        if: steps.changelog-check.outputs.changed == 'true'
+        uses: peter-evans/create-or-update-comment@e8674b075228eee787fea43ef493e45ece1004c9 # v5.0.0
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          body: >-
+            ⚠️ CHANGELOG.md was modified in this PR. Please do not modify CHANGELOG.md directly.
+            Instead, describe your change as a change-note. The CHANGELOG.md file will be automatically
+            generated from change-notes. For more information,
+            see [CONTRIBUTING.md](https://github.com/github/codeql-action/blob/main/CONTRIBUTING.md).
+
       - name: "Backport: Check out base ref"
         id: checkout-base
         if: ${{ startsWith(github.head_ref, 'backport-') }}