With this, we don't have to manually trigger backport whenever there is update to GitHub Actions dependencies.
Closes https://github.com/python/bedevere/issues/287
Let Dependabot update GitHub Actions dependency once a month. Here's reference to the dependabot configs. https://docs.github.com/en/free-pro-team@latest/github/administering-a-repository/keeping-your-actions-up-to-date-with-github-dependabot