**Apache Airflow version**:

2.0.1

**What happened**:

When clearing task across dags using `ExternalTaskMarker` the dag state of the external `DagRun` is not set to active. So cleared tasks in the external dag will not automatically start if the `DagRun` is a Failed or Succeeded state.

**What you expected to happen**:

The external `DagRun` run should also be set to Running state.

**How to reproduce it**:

Clear tasks in an external dag using an ExternalTaskMarker.


**Anything else we need to know**:

Looking at the code is has:

https://github.com/apache/airflow/blob/b23fc137812f5eabf7834e07e032915e2a504c17/airflow/models/dag.py#L1323-L1335

It seems like it intentionally calls the dag member method `set_dag_run_state` instead of letting the helper function `clear_task_insntances` set the `DagRun` state. But the member method will only change the state of `DagRun`s of dag where the original task is, while I believe `clear_task_instances` would correctly change the state of all involved `DagRun`s.

tests/sensors/test_external_task_sensor.py
op = ExternalTaskSensor(
            task_id='test_external_task_sensor_check',
            external_dag_id="non-existing-dag",
            external_task_id=None,
            check_existence=True,
            dag=self.dag,
        )
        with pytest.raises(AirflowException):
            op.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
class TestExternalTaskMarker(unittest.TestCase):
    def test_serialized_fields(self):
        assert {"recursion_depth"}.issubset(ExternalTaskMarker.get_serialized_fields())
    def test_serialized_external_task_marker(self):
        dag = DAG('test_serialized_external_task_marker', start_date=DEFAULT_DATE)
        task = ExternalTaskMarker(
            task_id="parent_task",
            external_dag_id="external_task_marker_child",
            external_task_id="child_task1",
            dag=dag,
        )
        serialized_op = SerializedBaseOperator.serialize_operator(task)
        deserialized_op = SerializedBaseOperator.deserialize_operator(serialized_op)
        assert deserialized_op.task_type == 'ExternalTaskMarker'
        assert getattr(deserialized_op, 'external_dag_id') == 'external_task_marker_child'
        assert getattr(deserialized_op, 'external_task_id') == 'child_task1'
@pytest.fixture
def dag_bag_ext():