**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
"""Serialization and deserialization should work for every DAG and Operator."""
        dags = collect_dags()
        serialized_dags = {}
        for _, v in dags.items():
            dag = SerializedDAG.to_dict(v)
            SerializedDAG.validate_schema(dag)
            serialized_dags[v.dag_id] = dag
        
        self.validate_serialized_dag(serialized_dags['simple_dag'], serialized_simple_dag_ground_truth)
    def validate_serialized_dag(self, json_dag, ground_truth_dag):
        """Verify serialized DAGs match the ground truth."""
        self.assertTrue(json_dag['dag']['fileloc'].split('/')[-1] == 'test_dag_serialization.py')
        json_dag['dag']['fileloc'] = None
        def sorted_serialized_dag(dag_dict: dict):
            """
            Sorts the "tasks" list and "access_control" permissions in the
            serialised dag python dictionary. This is needed as the order of
            items should not matter but assertEqual would fail if the order of
            items changes in the dag dictionary
            """
            dag_dict["dag"]["tasks"] = sorted(dag_dict["dag"]["tasks"], key=lambda x: sorted(x.keys()))
            dag_dict["dag"]["_access_control"]["__var"]["test_role"]["__var"] = sorted(
                dag_dict["dag"]["_access_control"]["__var"]["test_role"]["__var"]
            )
            return dag_dict
        assert sorted_serialized_dag(ground_truth_dag) == sorted_serialized_dag(json_dag)
    @pytest.mark.quarantined
    def test_deserialization_across_process(self):