Fix flaky spec

`I18n.available_locales=` does a little magic[1] and was causing some flakieness along the way, as the `:wl` locale persisted in future specs

Thanks for the heads up @javierm 👌

[1] https://www.rubydoc.info/github/svenfuchs/i18n/I18n%2FConfig:available_locales=

spec/features/localization_spec.rb

@@ -56,7 +56,7 @@ feature 'Localization' do
 
     before do
       I18n.enforce_available_locales = false
-      I18n.available_locales << :wl
+      I18n.available_locales = default_locales + [:wl]
       I18n.locale = :wl
     end