**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
"""OperatorLink not registered via Plugins nor a built-in OperatorLink"""
            name = 'My Link'
            def get_link(self, operator, dttm):
                return 'https://www.google.com'
        class MyOperator(BaseOperator):
            """Just a DummyOperator using above defined Extra Operator Link"""
            operator_extra_links = [TaskStateLink()]
            def execute(self, context):
                pass
        with DAG(dag_id='simple_dag', start_date=datetime(2019, 8, 1)) as dag:
            MyOperator(task_id='blah')
        serialized_dag = SerializedDAG.to_dict(dag)
        with self.assertLogs("airflow.serialization.serialized_objects", level="ERROR") as log_output:
            SerializedDAG.from_dict(serialized_dag)
            received_logs = log_output.output[0]
            expected_err_msg = (
                "Operator Link class 'tests.serialization.test_dag_serialization.TaskStateLink' "
                "not registered"
            )
            assert expected_err_msg in received_logs
    def test_extra_serialized_field_and_multiple_operator_links(self):