**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/dagrun.py
self, session: Session = None, execute_callbacks: bool = True
    ) -> Tuple[List[TI], Optional[callback_requests.DagCallbackRequest]]:
        """
        Determines the overall state of the DagRun based on the state
        of its TaskInstances.
        :param session: Sqlalchemy ORM Session
        :type session: Session
        :param execute_callbacks: Should dag callbacks (success/failure, SLA etc) be invoked
            directly (default: true) or recorded as a pending request in the ``callback`` property
        :type execute_callbacks: bool
        :return: Tuple containing tis that can be scheduled in the current loop & `callback` that
            needs to be executed
        """
        
        callback: Optional[callback_requests.DagCallbackRequest] = None
        start_dttm = timezone.utcnow()
        self.last_scheduling_decision = start_dttm
        with Stats.timer(f"dagrun.dependency-check.{self.dag_id}"):
            dag = self.get_dag()
            info = self.task_instance_scheduling_decisions(session)
            tis = info.tis
            schedulable_tis = info.schedulable_tis
            changed_tis = info.changed_tis
            finished_tasks = info.finished_tasks
            unfinished_tasks = info.unfinished_tasks
            none_depends_on_past = all(not t.task.depends_on_past for t in unfinished_tasks)
            none_task_concurrency = all(t.task.task_concurrency is None for t in unfinished_tasks)