figure out the minimal github token permissions for the `githubrepo` promise

[piontec]

It's really hard to find an answer to the question of which scopes are needed for such token. From the description, it seems we need admin permission, but some comments claim you don't need it. I think we just have to check in an experiment. admin is very broad, as it allows to delete any repo, so skipping it would be a great security improvement.