**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
"""Base metaclass of BaseOperator."""
    def __call__(cls, *args, **kwargs):
        """
        Called when you call BaseOperator(). In this way we are able to perform an action
        after initializing an operator no matter where  the ``super().__init__`` is called
        (before or after assign of new attributes in a custom operator).
        """
        obj: BaseOperator = type.__call__(cls, *args, **kwargs)
        
        obj.set_xcomargs_dependencies()
        
        obj._BaseOperator__instantiated = True
        return obj
@functools.total_ordering
class BaseOperator(Operator, LoggingMixin, TaskMixin, metaclass=BaseOperatorMeta):
    """