wiki repositories don't refresh because they're not part of the API

Description

While we can now clone wiki repositories in Desktop, there are some other corner cases (and console errors) that light up as a result of this.

Version

GitHub Desktop version: master - e.g. 77c2146e4094ed50904ecb0c378f245a000e6686 OS version: macOS Sierra 10.12.5

Steps to Reproduce

• Launch the app
• Add an existing GitHub wiki repository to the app via drag and drop
• Confirm it appears as a GitHub repository

• Peep the dev console, see the errors for all the nonexistent endpoints:
  • fetching issues
  • fetching mentionable users
  • fetching repository details
  • fetching the refresh interval from /repos/{owner}/{name}.wiki/git

This is using https://github.com/aspnet/Home/wiki

Expected behaviour: avoid fetching these endpoints for known cases Actual behaviour: lots of errors

Reproduces how often: I only tested this a couple of times, but I’m pretty sure it’s 100%

[shiftkey]

Related to this change, #4092 reports that wiki repositories are categorized as “Other”

[joshaber]

Yeah, that’s a good shout. I knew this was a problem but didn’t document it.