Fix delete branches (#119399)
Due to PR_WINDOW, if the magic string exists in the body but the pr was not updated recently, the query wouldn't find it and would delete the branch. Instead, query separately for branches with the no-delete-branch label, which I created recently.
Might as well query for branches with open PRs while we're at it so PRs with the stale label won't get their branches deleted either
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119399
Approved by: https://github.com/huydhn
