**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
count += (
                session.query(TI)
                .filter(
                    TI.dag_id == self.dag_id,
                    TI.execution_date == self.execution_date,
                    TI.task_id.in_(schedulable_ti_ids),
                )
                .update({TI.state: State.SCHEDULED}, synchronize_session=False)
            )
        
        if dummy_tis:
            count += (
                session.query(TI)
                .filter(
                    TI.dag_id == self.dag_id,
                    TI.execution_date == self.execution_date,
                    TI.task_id.in_(ti.task_id for ti in dummy_tis),
                )
                .update(
                    {
                        TI.state: State.SUCCESS,
                        TI.start_date: timezone.utcnow(),
                        TI.end_date: timezone.utcnow(),
                        TI.duration: 0,
                    },
                    synchronize_session=False,
                )
            )
        return count