**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
"""Generate Run ID based on Run Type and Execution Date"""
        return f"{run_type}__{execution_date.isoformat()}"
    @provide_session
    def get_task_instances(self, state=None, session=None):
        """Returns the task instances for this dag run"""
        tis = session.query(TI).filter(
            TI.dag_id == self.dag_id,
            TI.execution_date == self.execution_date,
        )
        if state:
            if isinstance(state, str):
                tis = tis.filter(TI.state == state)
            else:
                
                if None in state:
                    if all(x is None for x in state):
                        tis = tis.filter(TI.state.is_(None))
                    else:
                        not_none_state = [s for s in state if s]
                        tis = tis.filter(or_(TI.state.in_(not_none_state), TI.state.is_(None)))
                else:
                    tis = tis.filter(TI.state.in_(state))
        if self.dag and self.dag.partial:
            tis = tis.filter(TI.task_id.in_(self.dag.task_ids))
        return tis.all()
    @provide_session
    def get_task_instance(self, task_id: str, session: Session = None):