**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
tests/serialization/test_dag_serialization.py
dag = DAG(dag_id='simple_dag', start_date=datetime(2019, 8, 1), end_date=dag_end_date)
        BaseOperator(task_id='simple_task', dag=dag, end_date=task_end_date)
        serialized_dag = SerializedDAG.to_dict(dag)
        if not task_end_date or dag_end_date <= task_end_date:
            
            
            self.assertNotIn("end_date", serialized_dag["dag"]["tasks"][0])
        else:
            self.assertIn("end_date", serialized_dag["dag"]["tasks"][0])
        dag = SerializedDAG.from_dict(serialized_dag)
        simple_task = dag.task_dict["simple_task"]
        self.assertEqual(simple_task.end_date, expected_task_end_date)
    @parameterized.expand(
        [
            (None, None, None),
            ("@weekly", "@weekly", "0 0 * * 0"),
            ("@once", "@once", None),
            ({"__type": "timedelta", "__var": 86400.0}, timedelta(days=1), timedelta(days=1)),
        ]
    )
    def test_deserialization_schedule_interval(