Add role-specific user fabricators (#33437)

spec/controllers/admin/settings/branding_controller_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe Admin::Settings::BrandingController do
 
   describe 'When signed in as an admin' do
     before do
-      sign_in Fabricate(:user, role: UserRole.find_by(name: 'Admin')), scope: :user
+      sign_in Fabricate(:admin_user), scope: :user
     end
 
     describe 'PUT #update' do