langchain/agents/load_tools.py/_handle_callbacks
def _handle_callbacks(
    callback_manager: Optional[BaseCallbackManager], callbacks: Callbacks
) -> Callbacks:
    if callback_manager is not None:
        warnings.warn(
            "callback_manager is deprecated. Please use callbacks instead.",
            DeprecationWarning,
        )
        if callbacks is not None:
            raise ValueError(
                "Cannot specify both callback_manager and callbacks arguments."
            )
        return callback_manager
    return callbacks