**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
"""Returns dictionary of all global extra links"""
        from airflow import plugins_manager
        plugins_manager.initialize_extra_operators_links_plugins()
        if plugins_manager.global_operator_extra_links is None:
            raise AirflowException("Can't load operators")
        return {link.name: link for link in plugins_manager.global_operator_extra_links}
    @prepare_lineage
    def pre_execute(self, context: Any):
        """This hook is triggered right before self.execute() is called."""
    def execute(self, context: Any):
        """
        This is the main method to derive when creating an operator.
        Context is the same dictionary used as when rendering jinja templates.
        Refer to get_template_context for more context.
        """
        raise NotImplementedError()
    @apply_lineage
    def post_execute(self, context: Any, result: Any = None):
        """
        This hook is triggered right after self.execute() is called.
        It is passed the execution context and any results returned by the
        operator.
        """
    def on_kill(self) -> None: