Callback Output is not generating after task complete

[pip-install-skills]

I have created the tasks and added the python callable function, but I invoke the kickoff function after the task completion there is not txt file getting created, this is the version I'm using crewai==0.28.0

        def on_task_complete(task_result):
            file_path = "output.txt"
            with open(file_path, 'w') as file:
                file.write(task_result)


        task = Task(
            description=task_info.description,
            expected_output=task_info.expected_output,
            agent=agent,  # Assign the agent created on the go,
            callback=on_task_complete
        )

This is my code, please help