add more typing

examples/basic_generation.py

@@ -9,7 +9,7 @@ import asyncio
 import edge_tts
 
 
-async def main():
+async def main() -> None:
     TEXT = "Hello World!"
     VOICE = "en-GB-SoniaNeural"
     OUTPUT_FILE = "test.mp3"

examples/dynamic_voice_selection.py

@@ -11,7 +11,7 @@ import edge_tts
 from edge_tts import VoicesManager
 
 
-async def main():
+async def main() -> None:
     voices = await VoicesManager.create()
     voice = voices.find(Gender="Male", Language="es")
     # Also supports Locales