**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
"""Validate pickle in a subprocess."""
    dags = collect_dags(dag_folder)
    for dag in dags.values():
        queue.put(SerializedDAG.to_json(dag))
    queue.put(None)
class TestStringifiedDAGs(unittest.TestCase):
    """Unit tests for stringified DAGs."""
    def setUp(self):
        super().setUp()
        BaseHook.get_connection = mock.Mock(
            return_value=Connection(
                extra=(
                    '{'
                    '"project_id": "mock", '
                    '"location": "mock", '
                    '"instance": "mock", '
                    '"database_type": "postgres", '
                    '"use_proxy": "False", '
                    '"use_ssl": "False"'
                    '}'
                )
            )
        )
        self.maxDiff = None  
    def test_serialization(self):