**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/models/baseoperator.py
'_task_type',
                    'subdag',
                    'ui_color',
                    'ui_fgcolor',
                    'template_fields',
                    'template_fields_renderers',
                }
            )
            DagContext.pop_context_managed_dag()
        return cls.__serialized_fields
    def is_smart_sensor_compatible(self):
        """Return if this operator can use smart service. Default False."""
        return False
def chain(*tasks: Union[BaseOperator, Sequence[BaseOperator]]):
    r"""
    Given a number of tasks, builds a dependency chain.
    Support mix airflow.models.BaseOperator and List[airflow.models.BaseOperator].
    If you want to chain between two List[airflow.models.BaseOperator], have to
    make sure they have same length.
    .. code-block:: python
         chain(t1, [t2, t3], [t4, t5], t6)
    is equivalent to::
         / -> t2 -> t4 \
       t1               -> t6
         \ -> t3 -> t5 /
    .. code-block:: python
        t1.set_downstream(t2)
        t1.set_downstream(t3)
        t2.set_downstream(t4)
        t3.set_downstream(t5)