[core-workflow] last blocker for the GitHub migration is in!

Thanks to the very hard work of Maciej and Ezio, the final change required of bpo is in! That should be the last blocker for the migration. ( https://github.com/python/peps/blob/master/pep-0512.txt#L698 as always is the "official" todo list.) If there is any critical blocker that people feel *must* be in before the migration, *speak up now!* There will be a separate email about my current thinking on how to handle the migration.