### 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
self,
        content: Any,
        context: Dict,
        jinja_env: Optional[jinja2.Environment] = None,
        seen_oids: Optional[Set] = None,
    ) -> Any:
        """
        Render a templated string. The content can be a collection holding multiple templated strings and will
        be templated recursively.
        :param content: Content to template. Only strings can be templated (may be inside collection).
        :type content: Any
        :param context: Dict with values to apply on templated content
        :type context: dict
        :param jinja_env: Jinja environment. Can be provided to avoid re-creating Jinja environments during
            recursion.
        :type jinja_env: jinja2.Environment
        :param seen_oids: template fields already rendered (to avoid RecursionError on circular dependencies)
        :type seen_oids: set
        :return: Templated content
        """
        if not jinja_env:
            jinja_env = self.get_template_env()