**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
airflow/serialization/serialized_objects.py
#
            
            
            
            
            
            
            
            _operator_link_class_path, data = list(_operator_links_source.items())[0]
            if _operator_link_class_path in BUILTIN_OPERATOR_EXTRA_LINKS:
                single_op_link_class = import_string(_operator_link_class_path)
            elif _operator_link_class_path in plugins_manager.registered_operator_link_classes:
                single_op_link_class = plugins_manager.registered_operator_link_classes[
                    _operator_link_class_path
                ]
            else:
                log.error("Operator Link class %r not registered", _operator_link_class_path)
                return {}
            op_predefined_extra_link: BaseOperatorLink = cattr.structure(data, single_op_link_class)
            op_predefined_extra_links.update({op_predefined_extra_link.name: op_predefined_extra_link})
        return op_predefined_extra_links
    @classmethod
    def _serialize_operator_extra_links(cls, operator_extra_links: Iterable[BaseOperatorLink]):