**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
no_backfills: bool = False,
        run_type: Optional[DagRunType] = None,
        session: Session = None,
        execution_start_date: Optional[datetime] = None,
        execution_end_date: Optional[datetime] = None,
    ) -> List["DagRun"]:
        """
        Returns a set of dag runs for the given search criteria.
        :param dag_id: the dag_id or list of dag_id to find dag runs for
        :type dag_id: str or list[str]
        :param run_id: defines the run id for this dag run
        :type run_id: str
        :param run_type: type of DagRun
        :type run_type: airflow.utils.types.DagRunType
        :param execution_date: the execution date
        :type execution_date: datetime.datetime or list[datetime.datetime]
        :param state: the state of the dag run
        :type state: str
        :param external_trigger: whether this dag run is externally triggered
        :type external_trigger: bool
        :param no_backfills: return no backfills (True), return all (False).
            Defaults to False
        :type no_backfills: bool
        :param session: database session
        :type session: sqlalchemy.orm.session.Session
        :param execution_start_date: dag run that was executed from this date
        :type execution_start_date: datetime.datetime
        :param execution_end_date: dag run that was executed until this date
        :type execution_end_date: datetime.datetime
        """