**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
],
        )
        
        self.assertCountEqual(
            simple_task.extra_links,
            ['BigQuery Console #1', 'BigQuery Console #2', 'airflow', 'github', 'google'],
        )
        ti = TaskInstance(task=simple_task, execution_date=test_date)
        ti.xcom_push('search_query', ["dummy_value_1", "dummy_value_2"])
        
        custom_inbuilt_link = simple_task.get_extra_links(test_date, "BigQuery Console #1")
        self.assertEqual('https://console.cloud.google.com/bigquery?j=dummy_value_1', custom_inbuilt_link)
        
        custom_inbuilt_link = simple_task.get_extra_links(test_date, "BigQuery Console #2")
        self.assertEqual('https://console.cloud.google.com/bigquery?j=dummy_value_2', custom_inbuilt_link)
        
        google_link_from_plugin = simple_task.get_extra_links(test_date, GoogleLink.name)
        self.assertEqual("https://www.google.com", google_link_from_plugin)
    class ClassWithCustomAttributes:
        """
        Class for testing purpose: allows to create objects with custom attributes in one single statement.
        """
        def __init__(self, **kwargs):
            for key, value in kwargs.items():
                setattr(self, key, value)
        def __str__(self):
            return "{}({})".format(self.__class__.__name__, str(self.__dict__))
        def __repr__(self):
            return self.__str__()
        def __eq__(self, other):