When attempting to configuring a task, only non-forked GitHub repos appear in the list of available repos. Thus there does not seem to be a way to configure a new task for a forked repo.
It is somewhat unclear whether this is a bug or a feature. Are cloned repos meant to be prohibited?
Workaround: change the repo value in the form data and submit that.
Also it seems that there's an explicit filtering of forks happening.
repos = filter(lambda r: r.permissions.admin and not r.fork, repos)