Unable to consume data from broker using SASL_SSL and OAUTHBEARER mechanism

**Describe the bug**
Consumer throws an error when started

```sh
Heartbeat failed for group my-group because it is rebalancing
Unexpected error while fetching data: UnknownError
```

**Expected behaviour**
Consumer authenticates with the brokers and consumes the messages

**Environment (please complete the following information):**
- aiokafka version (`python -c "import aiokafka; print(aiokafka.__version__)"`): 0.8.0
- kafka-python version (`python -c "import kafka; print(kafka.__version__)"`): 2.0.2

**Reproducible example**
followed the example consumer script and provided additional information like `custom token provider`, `ssl_context`, `sasl_mechanism` and `security_protocol`