ci: update generate changelog pipeline to use app token (#423)

Author: nathanosdev

.github/workflows/generate-changelog.yml

@@ -9,6 +9,6 @@ jobs:
   generate_changelog:
     uses: dfinity/ci-tools/.github/workflows/generate-changelog.yaml@main
     with:
-      auto_merge: true
+      token_app_id: ${{ vars.PR_AUTOMATION_BOT_PUBLIC_APP_ID }}
     secrets:
-      token: ${{ secrets.GITHUB_TOKEN }}
+      token_private_key: ${{ secrets.PR_AUTOMATION_BOT_PUBLIC_PRIVATE_KEY }}