This commit adds the `stale-theme-pr-closer` closer action. This action is used to close theme pull requests with an `invalid` label that has been stale for a given number of `STALE_DAYS`.
Co-authored-by: Prashubh Atri <prashubh27@gmail.com> Co-authored-by: Prashubh Atri <prashubh27@gmail.com>