**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
DR = DagRun
        qry = session.query(DR)
        dag_ids = [dag_id] if isinstance(dag_id, str) else dag_id
        if dag_ids:
            qry = qry.filter(DR.dag_id.in_(dag_ids))
        if run_id:
            qry = qry.filter(DR.run_id == run_id)
        if execution_date:
            if isinstance(execution_date, list):
                qry = qry.filter(DR.execution_date.in_(execution_date))
            else:
                qry = qry.filter(DR.execution_date == execution_date)
        if execution_start_date and execution_end_date:
            qry = qry.filter(DR.execution_date.between(execution_start_date, execution_end_date))
        elif execution_start_date:
            qry = qry.filter(DR.execution_date >= execution_start_date)
        elif execution_end_date:
            qry = qry.filter(DR.execution_date <= execution_end_date)
        if state:
            qry = qry.filter(DR.state == state)
        if external_trigger is not None:
            qry = qry.filter(DR.external_trigger == external_trigger)
        if run_type:
            qry = qry.filter(DR.run_type == run_type)
        if no_backfills:
            qry = qry.filter(DR.run_type != DagRunType.BACKFILL_JOB)
        dr = qry.order_by(DR.execution_date).all()
        return dr
    @staticmethod
    def generate_run_id(run_type: DagRunType, execution_date: datetime) -> str: