Producers hangs while stopping in frozen datetime context

**Describe the bug**
Producers created in a frozen datetime context fail to stop properly (freezes). When freezing the datetime using https://github.com/spulec/freezegun.

**Expected behaviour**
Producers successfully start & stop.

**Environment (please complete the following information):**
- aiokafka version (`python -c "import aiokafka; print(aiokafka.__version__)"`): `0.11.0`
- Kafka Broker version (`kafka-topics.sh --version`): -
- Other information (Confluent Cloud version, etc.): -

**Reproducible example**
The code hangs in here: https://github.com/aio-libs/aiokafka/blob/master/aiokafka/producer/producer.py#L386