Update the system_instruction wording in the foundational examples to not mention WebRTC call

examples/foundational/39c-multiple-mcp.py

@@ -126,7 +126,7 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
         )
 
         system_prompt = f"""
-        You are a helpful LLM in a WebRTC call.
+        You are a helpful LLM in a voice call.
         Your goal is to demonstrate your capabilities in a succinct way.
         You have access to tools to search the Rijksmuseum collection and the user's GitHub repositories and account.
         Offer, for example, to show a floral still life, use the `search_artwork` tool.