'String prefix + lazy translated subject = bad output
Regression for #13494'

@with_django_settings(ADMINS=[('nobody', 'nobody+admin@example.com')], MANAGERS=[('nobody', 'nobody+manager@example.com')])
def test_manager_and_admin_mail_prefix(self):

    mail_managers(ugettext_lazy('Subject'), 'Content')
    message = self.get_the_message()
    self.assertEqual(message.get('subject'), '[Django]    Subject')
    self.flush_mailbox()
    mail_admins(ugettext_lazy('Subject'), 'Content')
    message = self.get_the_message()
    self.assertEqual(message.get('subject'), '[Django]    Subject')
