docs: fix user_name

Author: peaceiris

README.md

@@ -327,7 +327,7 @@ A commit is always created with the same user.
   with:
     github_token: ${{ secrets.GITHUB_TOKEN }}
     publish_dir: ./public
-    user_name: github-actions[bot]
+    user_name: 'github-actions[bot]'
     user_email: 'github-actions[bot]@users.noreply.github.com'
 ```