**Apache Airflow version**:
v2.0.0

**What happened**:

Custom operators inheriting from DummyOperator are go in to a scheduled state, where as DummyOperator itself is set straight to success.

**What you expected to happen**:

All operators should be successfully executed.

**How to reproduce it**:

```py
from datetime import datetime
from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator

class MyJob(DummyOperator):
    template_fields_renderers = {
        "body": "json"
    }
    template_fields = ("body",)

    def __init__(self, body, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.body = body

with DAG(
    dag_id="test",
    schedule_interval=None,
    start_date=datetime(2020, 8, 13),
) as dag:
    MyJob(task_id="aaaa", body={"aaa": "bbb"})

```

**Anything else we need to know**:
This is a known problem that we will fix, see: https://github.com/apache/airflow/pull/10956#discussion_r502492775
airflow/models/dagrun.py
return self._state
    def set_state(self, state):
        if self._state != state:
            self._state = state
            self.end_date = timezone.utcnow() if self._state in State.finished else None
    @declared_attr
    def state(self):
        return synonym('_state', descriptor=property(self.get_state, self.set_state))
    @provide_session
    def refresh_from_db(self, session: Session = None):
        """
        Reloads the current dagrun from the database
        :param session: database session
        :type session: Session
        """
        DR = DagRun
        exec_date = func.cast(self.execution_date, DateTime)
        dr = (
            session.query(DR)
            .filter(
                DR.dag_id == self.dag_id,
                func.cast(DR.execution_date, DateTime) == exec_date,
                DR.run_id == self.run_id,
            )
            .one()
        )
        self.id = dr.id
        self.state = dr.state
    @classmethod
    def next_dagruns_to_examine(