**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
"""
        Verify that all example DAGs work with DAG Serialization by
        checking fields between Serialized Dags & non-Serialized Dags
        """
        fields_to_check = dag.get_serialized_fields() - {
            
            'timezone',
            
            'default_args',
            "_task_group",
        }
        for field in fields_to_check:
            assert getattr(serialized_dag, field) == getattr(
                dag, field
            ), f'{dag.dag_id}.{field} does not match'
        if dag.default_args:
            for k, v in dag.default_args.items():
                if callable(v):
                    
                    assert k in serialized_dag.default_args
                else:
                    assert (
                        v == serialized_dag.default_args[k]
                    ), f'{dag.dag_id}.default_args[{k}] does not match'
        assert serialized_dag.timezone.name == dag.timezone.name
        for task_id in dag.task_ids:
            self.validate_deserialized_task(serialized_dag.get_task(task_id), dag.get_task(task_id))