**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
if max_number is None:
            max_number = cls.DEFAULT_DAGRUNS_TO_EXAMINE
        
        query = (
            session.query(cls)
            .filter(cls.state == State.RUNNING, cls.run_type != DagRunType.BACKFILL_JOB)
            .join(
                DagModel,
                DagModel.dag_id == cls.dag_id,
            )
            .filter(
                DagModel.is_paused.is_(False),
                DagModel.is_active.is_(True),
            )
            .order_by(
                nulls_first(cls.last_scheduling_decision, session=session),
                cls.execution_date,
            )
        )
        if not settings.ALLOW_FUTURE_EXEC_DATES:
            query = query.filter(DagRun.execution_date <= func.now())
        return with_row_locks(query.limit(max_number), of=cls, **skip_locked(session=session))
    @staticmethod
    @provide_session
    def find(
        dag_id: Optional[Union[str, List[str]]] = None,
        run_id: Optional[str] = None,
        execution_date: Optional[datetime] = None,
        state: Optional[str] = None,
        external_trigger: Optional[bool] = None,