error handling when populating 'create a git repository' dropdown

During the recent GitHub outages we've seen the project dropdown in 'create a git repository' not get properly populated.

It might be good to see if we can distinguish between an 'unsuccessful request' from a 'successful request returning no projects'. If so we could bubble that error up to the user, "github is acting out again, please try again later".

(of course there's further improvements possible, such as caching results from past successful calls, but imo just exposing the problem would already go a long way)

Start at the code that populates the project dropdown in “create a git repository” and trace how an unsuccessful GitHub request is represented versus a successful response with no projects. Reproduce the outage or failed-request behavior, then verify that the user sees a distinct error message while an empty successful response remains distinguishable.

Written by the indexing model from the issue text.