**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
"""
        Test that params work both on Serialized DAGs & Tasks
        """
        dag = DAG(dag_id='simple_dag')
        BaseOperator(task_id='simple_task', dag=dag, params=val, start_date=datetime(2019, 8, 1))
        serialized_dag = SerializedDAG.to_dict(dag)
        if val:
            self.assertIn("params", serialized_dag["dag"]["tasks"][0])
        else:
            self.assertNotIn("params", serialized_dag["dag"]["tasks"][0])
        deserialized_dag = SerializedDAG.from_dict(serialized_dag)
        deserialized_simple_task = deserialized_dag.task_dict["simple_task"]
        self.assertEqual(expected_val, deserialized_simple_task.params)
    def test_extra_serialized_field_and_operator_links(self):
        """
        Assert extra field exists & OperatorLinks defined in Plugins and inbuilt Operator Links.
        This tests also depends on GoogleLink() registered as a plugin
        in tests/plugins/test_plugin.py
        The function tests that if extra operator links are registered in plugin
        in ``operator_extra_links`` and the same is also defined in
        the Operator in ``BaseOperator.operator_extra_links``, it has the correct
        extra link.
        """
        test_date = datetime(2019, 8, 1)
        dag = DAG(dag_id='simple_dag', start_date=test_date)