Producers hangs while stopping in frozen datetime context

[mdczaplicki]

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