oauth_login_spec.rb

- I tried to get this to work by stubbing out portions of the config within the
  test. This didn't work as expected because Devise/Omniauth loaded before the
  stub could run, and the stubbed config was ignored.

- I attempted to fix this by reloading Devise/Omniauth after stubbing the
  config. This successfully got Devise to load the stubbed providers, but failed
  while trying to access a route such as `user_gitlab_omniauth_authorize_path`.

- I spent a while trying to figure this out (even trying
  `Rails.application.reload_routes!`), but nothing seemed to work.

- I settled for adding this config directly to `gitlab.yml` rather than go down
  this path any further.