Not doing so might cause the following test to use translations for
only one locale. This scenario happens if the previous test executes
I18n.reload!, which resets I18n.config.backend's "@translations"
instance variable.
So, the sequence could be as follows:
1. The previous tests sets `@translations = nil`
2. This test stubs `available_locales` to `[:en]`
3. `@translations` gets only translations for `en`
4. The following test doesn't find translations for Spanish and fails
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