**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
"""The previous DagRun, if there is one"""
        filters = [
            DagRun.dag_id == self.dag_id,
            DagRun.execution_date < self.execution_date,
        ]
        if state is not None:
            filters.append(DagRun.state == state)
        return session.query(DagRun).filter(*filters).order_by(DagRun.execution_date.desc()).first()
    @provide_session
    def get_previous_scheduled_dagrun(self, session: Session = None):
        """The previous, SCHEDULED DagRun, if there is one"""
        dag = self.get_dag()
        return (
            session.query(DagRun)
            .filter(
                DagRun.dag_id == self.dag_id,
                DagRun.execution_date == dag.previous_schedule(self.execution_date),
            )
            .first()
        )
    @provide_session
    def update_state(