**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
from airflow.models.dagparam import DagParam
        from airflow.models.xcom_arg import XComArg
        if isinstance(content, str):
            if any(content.endswith(ext) for ext in self.template_ext):
                
                return jinja_env.get_template(content).render(**context)
            else:
                return jinja_env.from_string(content).render(**context)
        elif isinstance(content, (XComArg, DagParam)):
            return content.resolve(context)
        if isinstance(content, tuple):
            if type(content) is not tuple:  
                
                return content.__class__(
                    *(self.render_template(element, context, jinja_env) for element in content)  
                )
            else:
                return tuple(self.render_template(element, context, jinja_env) for element in content)
        elif isinstance(content, list):
            return [self.render_template(element, context, jinja_env) for element in content]
        elif isinstance(content, dict):
            return {key: self.render_template(value, context, jinja_env) for key, value in content.items()}
        elif isinstance(content, set):
            return {self.render_template(element, context, jinja_env) for element in content}
        else:
            if seen_oids is None:
                seen_oids = set()
            self._render_nested_template_fields(content, context, jinja_env, seen_oids)
            return content
    def _render_nested_template_fields(