### 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
from airflow.models.dagparam import DagParam
        from airflow.models.xcom_arg import XComArg
        if isinstance(content, str):
            if any(content.endswith(ext) for ext in self.template_ext):
                
                return jinja_env.get_template(content).render(**context)
            else:
                return jinja_env.from_string(content).render(**context)
        elif isinstance(content, (XComArg, DagParam)):
            return content.resolve(context)
        if isinstance(content, tuple):
            if type(content) is not tuple:
                
                return content.__class__(
                    *(self.render_template(element, context, jinja_env) for element in content)
                )
            else:
                return tuple(self.render_template(element, context, jinja_env) for element in content)
        elif isinstance(content, list):
            return [self.render_template(element, context, jinja_env) for element in content]
        elif isinstance(content, dict):
            return {key: self.render_template(value, context, jinja_env) for key, value in content.items()}
        elif isinstance(content, set):
            return {self.render_template(element, context, jinja_env) for element in content}
        else:
            if seen_oids is None:
                seen_oids = set()
            self._render_nested_template_fields(content, context, jinja_env, seen_oids)
            return content
    def _render_nested_template_fields(