**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
#
#
#
from datetime import datetime
from typing import Any, Iterable, List, NamedTuple, Optional, Tuple, Union
from sqlalchemy import (
    Boolean,
    Column,
    DateTime,
    Index,
    Integer,
    PickleType,
    String,
    UniqueConstraint,
    and_,
    func,
    or_,
)
from sqlalchemy.exc import IntegrityError
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.orm import backref, relationship, synonym
from sqlalchemy.orm.session import Session
from airflow import settings