**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
nested1=ClassWithCustomAttributes(
                        att1="{{ task.task_id }}", att2="{{ task.task_id }}", template_fields=["att1"]
                    ),
                    nested2=ClassWithCustomAttributes(
                        att3="{{ task.task_id }}", att4="{{ task.task_id }}", template_fields=["att3"]
                    ),
                    template_fields=["nested1"],
                ),
                "ClassWithCustomAttributes("
                "{'nested1': ClassWithCustomAttributes({'att1': '{{ task.task_id }}', "
                "'att2': '{{ task.task_id }}', 'template_fields': ['att1']}), "
                "'nested2': ClassWithCustomAttributes({'att3': '{{ task.task_id }}', 'att4': "
                "'{{ task.task_id }}', 'template_fields': ['att3']}), 'template_fields': ['nested1']})",
            ),
        ]
    )
    def test_templated_fields_exist_in_serialized_dag(self, templated_field, expected_field):
        """
        Test that templated_fields exists for all Operators in Serialized DAG
        Since we don't want to inflate arbitrary python objects (it poses a RCE/security risk etc.)
        we want check that non-"basic" objects are turned in to strings after deserializing.
        """
        dag = DAG("test_serialized_template_fields", start_date=datetime(2019, 8, 1))
        with dag:
            BashOperator(task_id="test", bash_command=templated_field)
        serialized_dag = SerializedDAG.to_dict(dag)
        deserialized_dag = SerializedDAG.from_dict(serialized_dag)
        deserialized_test_task = deserialized_dag.task_dict["test"]
        self.assertEqual(expected_field, getattr(deserialized_test_task, "bash_command"))
    def test_dag_serialized_fields_with_schema(self):