Fix for #574
@rm-openai I'm not sure how to add a test within the repo but I have
pasted a test script below that seems to work
```python
import asyncio
from openai.types.responses import ResponseTextDeltaEvent
from agents import Agent, Runner
async def main():
agent = Agent(
name="Joker",
instructions="You are a helpful assistant.",
)
result = Runner.run_streamed(agent, input="Please tell me 5 jokes.")
num_visible_event = 0
async for event in result.stream_events():
if event.type == "raw_response_event" and isinstance(event.data, ResponseTextDeltaEvent):
print(event.data.delta, end="", flush=True)
num_visible_event += 1
print(num_visible_event)
if num_visible_event == 3:
result.cancel()
if __name__ == "__main__":
asyncio.run(main())
````
