### 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
doc_md: Optional[str] = None,
        doc_json: Optional[str] = None,
        doc_yaml: Optional[str] = None,
        doc_rst: Optional[str] = None,
        **kwargs,
    ):
        from airflow.models.dag import DagContext
        from airflow.utils.task_group import TaskGroupContext
        super().__init__()
        if kwargs:
            if not conf.getboolean('operators', 'ALLOW_ILLEGAL_ARGUMENTS'):
                raise AirflowException(
                    "Invalid arguments were passed to {c} (task_id: {t}). Invalid "
                    "arguments were:\n**kwargs: {k}".format(c=self.__class__.__name__, k=kwargs, t=task_id),
                )
            warnings.warn(
                'Invalid arguments were passed to {c} (task_id: {t}). '
                'Support for passing such arguments will be dropped in '
                'future. Invalid arguments were:'
                '\n**kwargs: {k}'.format(c=self.__class__.__name__, k=kwargs, t=task_id),
                category=PendingDeprecationWarning,
                stacklevel=3,
            )
        validate_key(task_id)
        self.task_id = task_id
        self.label = task_id
        task_group = task_group or TaskGroupContext.get_current_task_group(dag)
        if task_group:
            self.task_id = task_group.child_id(task_id)
            task_group.add(self)