There could be cause for legal action against Github over this, since one could not reasonably expect that using Github's own "Sign in with Github" could allow the site you are logging into to automatically cause actions on your behalf that would result in your account being banned. Contact a lawyer.
Another possible legal angle is that by providing these powers to websites with little or no oversight and "people wil just gloss over it" UX, they are facilitating the very star farming they are banning over.
Another possible legal angle is that by providing these powers to websites with little or no oversight and "people wil just gloss over it" UX, they are facilitating the very star farming they are banning over.