Update app.py

app.py

@@ -117,7 +117,7 @@ async def greet(product,description):
           - content safety check output $model=llama_guard
 
     prompts:
-      - task: content_safety_check_input $model=main
+      - task: content_safety_check_input $model=shield
         content: |
           You are a policy expert trying to help determine whether a user prompt is in
           violation of the defined safety policies.