### Apache Airflow version

2.1.3 (latest released)

### Operating System

Debian Buster

### Versions of Apache Airflow Providers

_No response_

### Deployment

Managed Services (Astronomer, Composer, MWAA etc.)

### Deployment details

Running `quay.io/astronomer/ap-airflow:2.1.3-buster` Docker image

### What happened

In the task attributes view of a BashOperator, the `template_ext` row doesn't show any value, while I would expect to see `('.sh', '.bash')`.

![image](https://user-images.githubusercontent.com/6249654/131467817-8620f68d-0f3d-491d-ad38-cbf5b91cdcb3.png)


### What you expected to happen

Expect to see correct `template_ext` value

### How to reproduce

Run a BashOperator and browse to Instance Details --> scroll down to `template_ext` row

### Anything else

Spent a little time trying to figure out what could be the reason, but haven't found the problem yet. Therefore created issue to track.

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/models/baseoperator.py
)
            DagContext.pop_context_managed_dag()
        return cls.__serialized_fields
    def is_smart_sensor_compatible(self):
        """Return if this operator can use smart service. Default False."""
        return False
    @property
    def inherits_from_dummy_operator(self):
        """Used to determine if an Operator is inherited from DummyOperator"""
        
        
        
        return getattr(self, '_is_dummy', False)
    def defer(
        self,
        *,
        trigger: BaseTrigger,
        method_name: str,
        kwargs: Optional[Dict[str, Any]] = None,
        timeout: Optional[timedelta] = None,
    ):
        """
        Marks this Operator as being "deferred" - that is, suspending its
        execution until the provided trigger fires an event.
        This is achieved by raising a special exception (TaskDeferred)
        which is caught in the main _execute_task wrapper.
        """
        raise TaskDeferred(trigger=trigger, method_name=method_name, kwargs=kwargs, timeout=timeout)
Chainable = Union[BaseOperator, "XComArg", EdgeModifier]
def chain(*tasks: Union[Chainable, Sequence[Chainable]]) -> None: