Fix an issue with some examples where punctuation was missing from the LLM output, by tweaking the LLM prompt.

examples/foundational/14n-function-calling-perplexity.py

@@ -77,7 +77,7 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     messages = [
         {
             "role": "user",
-            "content": "You are a helpful LLM in a WebRTC call. Your goal is to demonstrate your capabilities in a succinct way. Your output will be converted to audio so don't include special characters in your answers. Respond to what the user said in a creative and helpful way, but try to be brief.",
+            "content": "You are a helpful LLM in a WebRTC call. Your goal is to demonstrate your capabilities in a succinct way. Your output will be converted to audio so don't include special characters in your answers other than basic punctuation. Respond to what the user said in a creative and helpful way, but try to be brief.",
         },
     ]