I guess, line 59 in file "[airflow/airflow/task/task_runner/__init__.py](https://github.com/apache/airflow/blob/5a864f0e456348e0a871cf4678e1ffeec541c52d/airflow/task/task_runner/__init__.py#L59)" should change like:

**OLD**: f'The task runner could not be loaded. Please check "executor" key in "core" section.'
**NEW**: f'The task runner could not be loaded. Please check "task_runner" key in "core" section.'

So, "executor" should be replaced with "task_runner".
airflow/task/task_runner/__init__.py
#
#
#
import logging
from airflow.configuration import conf
from airflow.exceptions import AirflowConfigException
from airflow.utils.module_loading import import_string
log = logging.getLogger(__name__)
_TASK_RUNNER_NAME = conf.get('core', 'TASK_RUNNER')
STANDARD_TASK_RUNNER = "StandardTaskRunner"
CGROUP_TASK_RUNNER = "CgroupTaskRunner"
CORE_TASK_RUNNERS = {
    STANDARD_TASK_RUNNER: "airflow.task.task_runner.standard_task_runner.StandardTaskRunner",
    CGROUP_TASK_RUNNER: "airflow.task.task_runner.cgroup_task_runner.CgroupTaskRunner",
}
def get_task_runner(local_task_job):