update apikey handling

app.py

@@ -56,9 +56,7 @@ tool_list.columns = ['Tool', 'Description']
 def on_api_key_change():
     api_key = ss.get('api_key') or os.getenv('OPENAI_API_KEY')
     # Check if key is valid
-    if oai_key_isvalid(api_key):
-        os.environ["OPENAI_API_KEY"] = api_key
-    else:
+    if not oai_key_isvalid(api_key):
         st.write("Please input a valid OpenAI API key.")
 
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