fix(tests): provide LOCALES on TestVoiceModePreferenceGate

PR #2067 made TestVoiceModePreferenceGate.test_settings_pane_has_voice_mode_i18n_keys
adaptive via self.LOCALES but only defined LOCALES on the sibling class
TestComposerVoiceButtonI18n. AttributeError on CI.

Mirror the tuple to TestVoiceModePreferenceGate so the count assert resolves
to 10 with Italian present.

Co-authored-by: Samuel Gudi <samuel.gudi.official@gmail.com>

tests/test_issue1488_composer_voice_buttons.py

@@ -171,6 +171,8 @@ class TestComposerVoiceButtonI18n:
 class TestVoiceModePreferenceGate:
     """boot.js must hide btnVoiceMode by default, surface it via Preferences."""
 
+    LOCALES = ("en", "it", "ja", "ru", "es", "de", "zh", "zh-Hant", "pt", "ko")
+
     def test_voice_mode_pref_is_localstorage_backed(self):
         """The pref reads from localStorage key 'hermes-voice-mode-button'."""
         src = _src("boot.js")