**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
"""
        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)
        CustomOperator(task_id='simple_task', dag=dag, bash_command=["echo", "true"])
        serialized_dag = SerializedDAG.to_dict(dag)
        self.assertIn("bash_command", serialized_dag["dag"]["tasks"][0])
        dag = SerializedDAG.from_dict(serialized_dag)
        simple_task = dag.task_dict["simple_task"]
        self.assertEqual(getattr(simple_task, "bash_command"), ["echo", "true"])
        
        
        
        
        self.assertEqual(
            serialized_dag["dag"]["tasks"][0]["_operator_extra_links"],
            [
                {'tests.test_utils.mock_operators.CustomBaseIndexOpLink': {'index': 0}},
                {'tests.test_utils.mock_operators.CustomBaseIndexOpLink': {'index': 1}},