**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
if self._process is None:
            raise AirflowException("Tried to kill process before starting!")
        if self._process.is_alive() and self._process.pid:
            self.log.warning("Killing DAGFileProcessorProcess (PID=%d)", self._process.pid)
            os.kill(self._process.pid, signal.SIGKILL)
        if self._parent_channel:
            self._parent_channel.close()
    @property
    def pid(self) -> int:
        """
        :return: the PID of the process launched to process the given file
        :rtype: int
        """
        if self._process is None or self._process.pid is None:
            raise AirflowException("Tried to get PID before starting!")
        return self._process.pid
    @property
    def exit_code(self) -> Optional[int]:
        """
        After the process is finished, this can be called to get the return code
        :return: the exit code of the process
        :rtype: int
        """
        if self._process is None:
            raise AirflowException("Tried to get exit code before starting!")
        if not self._done:
            raise AirflowException("Tried to call retcode before process was finished!")
        return self._process.exitcode
    @property
    def done(self) -> bool: