**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
"""A serialized DAG can be deserialized in another process."""
        
        
        
        queue = multiprocessing.Queue()
        proc = multiprocessing.Process(target=serialize_subprocess, args=(queue, "airflow/example_dags"))
        proc.daemon = True
        proc.start()
        stringified_dags = {}
        while True:
            v = queue.get()
            if v is None:
                break
            dag = SerializedDAG.from_json(v)
            self.assertTrue(isinstance(dag, DAG))
            stringified_dags[dag.dag_id] = dag
        dags = collect_dags("airflow/example_dags")
        assert set(stringified_dags.keys()) == set(dags.keys())
        
        for dag_id in stringified_dags:
            self.validate_deserialized_dag(stringified_dags[dag_id], dags[dag_id])
    def test_roundtrip_provider_example_dags(self):