fix union type error for python < 3.12

src/streamlit_app.py

@@ -2,7 +2,7 @@ import streamlit as st
 import asyncio
 from dotenv import load_dotenv
 load_dotenv()
-
+from typing import Union
 from config import languages, voice_names, default_speaker_1, default_speaker_2, articles
 from script_generation import MarkdownToScrip, ScriptConfig, PodScript
 from audio_generation import ScriptToAudio, AudioConfig
@@ -24,7 +24,7 @@ async def generate_audio(script: PodScript, voice1: str, voice2: str):
     return await generator.run(script, voice1, voice2)
 
 # Sync wrappers for Streamlit
-def generate_script_sync(article: str, language: str, voice1: str, voice2: str) -> PodScript | None:
+def generate_script_sync(article: str, language: str, voice1: str, voice2: str) ->  Union[PodScript, None]:
     return asyncio.run(generate_script(article, language, voice1, voice2))
 
 def generate_audio_sync(script: PodScript, voice1: str, voice2: str):