[GHF] Small cleanup
- Use double quotes for Python string literals (per https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#strings )
- Do not add label if merge_on_green is called with dry_run argument
- Dismantle pyramid of doom (and avoid infinite while) by specifying
timeout as exit criteria
- Use `handle_exception` for revert workflow as well
- Do not double post comment if merge_on_green times out
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77004
Approved by: https://github.com/mehtanirav
