**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
"ui_color": "#fff",
                "ui_fgcolor": "#000",
                "template_fields": ['bash_command'],
                "template_fields_renderers": {},
                "_task_type": "CustomOperator",
                "_task_module": "tests.test_utils.mock_operators",
                "pool": "default_pool",
                'label': 'custom_task',
            },
        ],
        "timezone": "UTC",
        "_access_control": {
            "__type": "dict",
            "__var": {
                "test_role": {
                    "__type": "set",
                    "__var": [permissions.ACTION_CAN_READ, permissions.ACTION_CAN_EDIT],
                }
            },
        },
    },
}
ROOT_FOLDER = os.path.realpath(
    os.path.join(os.path.dirname(os.path.realpath(__file__)), os.pardir, os.pardir)
)
def make_example_dags(module_path):
    """Loads DAGs from a module for test."""
    dagbag = DagBag(module_path)
    return dagbag.dags
def make_simple_dag():