**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.__dict__ = state  
        self._log = logging.getLogger("airflow.task.operators")
    def render_template_fields(self, context: Dict, jinja_env: Optional[jinja2.Environment] = None) -> None:
        """
        Template all attributes listed in template_fields. Note this operation is irreversible.
        :param context: Dict with values to apply on content
        :type context: dict
        :param jinja_env: Jinja environment
        :type jinja_env: jinja2.Environment
        """
        if not jinja_env:
            jinja_env = self.get_template_env()
        self._do_render_template_fields(self, self.template_fields, context, jinja_env, set())
    def _do_render_template_fields(
        self,
        parent: Any,
        template_fields: Iterable[str],
        context: Dict,
        jinja_env: jinja2.Environment,
        seen_oids: Set,
    ) -> None:
        for attr_name in template_fields:
            content = getattr(parent, attr_name)
            if content:
                rendered_content = self.render_template(content, context, jinja_env, seen_oids)
                setattr(parent, attr_name, rendered_content)
    def render_template(