fix: correct Gemini TTS voice names

tests/test_google_tts.py

@@ -0,0 +1,10 @@
+from pipecat.services.google.tts import GeminiTTSService
+
+
+def test_gemini_tts_available_voices_match_documented_names():
+    voices = GeminiTTSService.AVAILABLE_VOICES
+
+    assert "Callirrhoe" in voices
+    assert "Sulafat" in voices
+    assert "Callirhoe" not in voices
+    assert "Sulafar" not in voices