Prevent ApplicationHelper specs from polluting later ones

We don't want the locale to be set to Brazilian Portuguese for any subsequent
specs!

spec/helpers/application_helper_spec.rb

@@ -312,9 +312,9 @@ describe ApplicationHelper do
 
   describe '#locale_path' do
     it 'returns the locale path with an `_`' do
-      Gitlab::I18n.locale = 'pt-BR'
-
+      Gitlab::I18n.with_locale('pt-BR') do
         expect(helper.locale_path).to include('assets/locale/pt_BR/app')
       end
     end
+  end
 end