**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
"""@property: list of tasks directly upstream"""
        return [self.dag.get_task(tid) for tid in self._upstream_task_ids]
    @property
    def upstream_task_ids(self) -> Set[str]:
        """@property: set of ids of tasks directly upstream"""
        return self._upstream_task_ids
    @property
    def downstream_list(self) -> List["BaseOperator"]:
        """@property: list of tasks directly downstream"""
        return [self.dag.get_task(tid) for tid in self._downstream_task_ids]
    @property
    def downstream_task_ids(self) -> Set[str]:
        """@property: set of ids of tasks directly downstream"""
        return self._downstream_task_ids
    @provide_session
    def clear(