Link to GitHub failed: Permission Denied!

I'm trying to link Keybase to my Github and posted a public gist [keybase.md](https://gist.github.com/ca468oo7/5530f6dc021c45ef5823b90e7e7ca45f). The app won't recognize it and the command line keeps saying "Permission Denied! Make sure your gist is public!" but the gist is already public.

Start by reproducing the GitHub linking flow with the public keybase.md gist and the command-line client, then trace where the permission-denied result is produced. Done means a genuinely public GitHub gist is recognized without the incorrect permission error, with coverage for this reported case.

Written by the indexing model from the issue text.