**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
"""Collects DAGs to test."""
    dags = {}
    dags.update(make_simple_dag())
    dags.update(make_user_defined_macro_filter_dag())
    if dag_folder:
        if isinstance(dag_folder, (list, tuple)):
            patterns = dag_folder
        else:
            patterns = [dag_folder]
    else:
        patterns = [
            "airflow/example_dags",
            "airflow/providers/*/example_dags",
            "airflow/providers/*/*/example_dags",
        ]
    for pattern in patterns:
        for directory in glob(f"{ROOT_FOLDER}/{pattern}"):
            dags.update(make_example_dags(directory))
    
    dags = {dag_id: dag for dag_id, dag in dags.items() if not dag.is_subdag}
    return dags
def serialize_subprocess(queue, dag_folder):