Fix typo in task_runner for ``AirflowConfigException`` (#15067)
Fix typo in task_runner for ``AirflowConfigException`` (#15067)

Key name "executor" has changed to "task_runner" since this value does not belong to the executor, but the task_runner.

This PR fixes the typo in the exception message.

closes: #14933
nathanielvarona/airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,apache/airflow,sekikn/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,lyft/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,apache/incubator-airflow,bolkedebruin/airflow,dhuang/incubator-airflow,mistercrunch/airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,apache/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,lyft/incubator-airflow,apache/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow