Transactional Example not working

I have tried the [transaction_example example](https://aiokafka.readthedocs.io/en/stable/examples/transaction_example.html) provided in the documentation and it does not work. After checking the code, I see that the it get stuck when starting the producer in [await self._sender.start()](https://github.com/aio-libs/aiokafka/blob/master/aiokafka/producer/producer.py#L369). I added some logs after `await producer.start()` in the example and they are never shown.

Context:

- `python`: 3.12
- `aiokafka`: 0.12
- `docker image`: confluentinc/cp-kafka:7.7.0 (kafka 3.7.x)

After I removed everything related with `transactions` the code works.

Any ideas what is happening?