**Apache Airflow version**:

1.10.12

**What happened**:

I created dag with dagrun_timeout=2 minutes. 

After 2 minutes dagrun is marked as failed and the next one is started, but task keeps going.

**What you expected to happen**:

Task is killed with dag run as it is done when you mark dagrun failed manually.

**How to reproduce it**:
```
dag = DAG(dag_id='platform.airflow-test',
          description='',
          schedule_interval="0 0 * * *",
          start_date=datetime(2020, 7, 1),
          max_active_runs=1,
          catchup=True,
          dagrun_timeout=timedelta(minutes=2))

run_this = BashOperator(
    task_id='run_after_loop',
    bash_command=' for((i=1;i<=600;i+=1)); do echo "Welcome $i times"; sleep 1;  done',
    dag=dag,
)
```
airflow/jobs/scheduler_job.py
self._kill_process()
        if not self._process.is_alive():
            self._done = True
            self.log.debug("Waiting for %s", self._process)
            self._process.join()
            self._parent_channel.close()
            return True
        return False
    @property
    def result(self) -> Optional[Tuple[int, int]]:
        """
        :return: result of running DagFileProcessor.process_file()
        :rtype: tuple[int, int] or None
        """
        if not self.done:
            raise AirflowException("Tried to get the result before it's done!")
        return self._result
    @property
    def start_time(self) -> datetime.datetime:
        """
        :return: when this started to process the file
        :rtype: datetime
        """
        if self._start_time is None:
            raise AirflowException("Tried to get start time before it started!")
        return self._start_time
    @property
    def waitable_handle(self):
        return self._process.sentinel
class DagFileProcessor(LoggingMixin):