**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
try:
                children = node.children.values()
            except AttributeError:
                
                expected_serialized = SerializedBaseOperator.serialize_operator(dag.get_task(node.task_id))
                expected_deserialized = SerializedBaseOperator.deserialize_operator(expected_serialized)
                expected_dict = SerializedBaseOperator.serialize_operator(expected_deserialized)
                assert node
                assert SerializedBaseOperator.serialize_operator(node) == expected_dict
                return
            for child in children:
                check_task_group(child)
        check_task_group(serialized_dag.task_group)
def test_kubernetes_optional():