**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
"""
        Get list of the direct relatives to the current task, upstream or
        downstream.
        """
        if upstream:
            return self.upstream_list
        else:
            return self.downstream_list
    def __repr__(self):
        return "<Task({self.task_type}): {self.task_id}>".format(self=self)
    @property
    def task_type(self) -> str:
        """@property: type of the task"""
        return self.__class__.__name__
    def add_only_new(self, item_set: Set[str], item: str) -> None:
        """Adds only new items to item set"""
        if item in item_set:
            self.log.warning('Dependency %s, %s already registered', self, item)
        else:
            item_set.add(item)
    @property
    def roots(self) -> List["BaseOperator"]: