Describe the bug
After update to 1.15.0, the gradio ui seems to broken.

Code to reproduce the error

from smolagents import CodeAgent, GradioUI, OpenAIServerModel


agent = CodeAgent(
    tools=[],
    model=OpenAIServerModel(
        ...
    ),
    verbosity_level=1,
    name="example_agent",
    description="This is an example agent.",
    step_callbacks=[],
    stream_outputs=True, # or False
)

GradioUI(agent, file_upload_folder="./data").launch()

Error logs (if any)

1. when stream_outputs=True, the message will display twice.

2. when stream_outputs=False, the message will nerver display.

Expected behavior
A clear and concise description of what you expected to happen.

Packages version:
1.15.0

Additional context
Add any other context about the problem here.