Allow remote translation tests to be run offline

The method `available_locales` in
`RemoteTranslations::Microsoft::AvailableLocales` needs to execute a
request to an external server in order to work, meaning it will fail if
the machine its executed on doesn't have an internet connection.

So we're stubbing the method in the tests using it.

spec/controllers/remote_translation_controller_spec.rb

@@ -1,6 +1,6 @@
 require "rails_helper"
 
-describe RemoteTranslationsController do
+describe RemoteTranslationsController, :remote_translations do
   describe "POST create", :delay_jobs do
     let(:debate) { create(:debate) }