**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
if isinstance(arg, XComArg):
                self.set_upstream(arg.operator)
            elif isinstance(arg, (tuple, set, list)):
                for elem in arg:
                    apply_set_upstream(elem)
            elif isinstance(arg, dict):
                for elem in arg.values():
                    apply_set_upstream(elem)
            elif hasattr(arg, "template_fields"):
                for elem in arg.template_fields:
                    apply_set_upstream(elem)
        for field in self.template_fields:
            if hasattr(self, field):
                arg = getattr(self, field)
                apply_set_upstream(arg)
    @property
    def priority_weight_total(self) -> int:
        """
        Total priority weight for the task. It might include all upstream or downstream tasks.
        depending on the weight rule.
          - WeightRule.ABSOLUTE - only own weight
          - WeightRule.DOWNSTREAM - adds priority weight of all downstream tasks
          - WeightRule.UPSTREAM - adds priority weight of all upstream tasks
        """
        if self.weight_rule == WeightRule.ABSOLUTE:
            return self.priority_weight
        elif self.weight_rule == WeightRule.DOWNSTREAM:
            upstream = False
        elif self.weight_rule == WeightRule.UPSTREAM: