**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
self.retry_delay = retry_delay
        else:
            self.log.debug("Retry_delay isn't timedelta object, assuming secs")
            self.retry_delay = timedelta(seconds=retry_delay)  
        self.retry_exponential_backoff = retry_exponential_backoff
        self.max_retry_delay = max_retry_delay
        self.params = params or {}  
        self.priority_weight = priority_weight
        if not WeightRule.is_valid(weight_rule):
            raise AirflowException(
                "The weight_rule must be one of {all_weight_rules},"
                "'{d}.{t}'; received '{tr}'.".format(
                    all_weight_rules=WeightRule.all_weight_rules,
                    d=dag.dag_id if dag else "",
                    t=task_id,
                    tr=weight_rule,
                )
            )
        self.weight_rule = weight_rule
        self.resources: Optional[Resources] = Resources(**resources) if resources else None
        self.run_as_user = run_as_user
        self.task_concurrency = task_concurrency
        self.executor_config = executor_config or {}
        self.do_xcom_push = do_xcom_push
        
        self._upstream_task_ids: Set[str] = set()
        self._downstream_task_ids: Set[str] = set()
        self._dag = None
        self.dag = dag or DagContext.get_current_dag()