### 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
"""Performs dry run for the operator - just render template fields."""
        self.log.info('Dry run')
        for field in self.template_fields:
            content = getattr(self, field)
            if content and isinstance(content, str):
                self.log.info('Rendering template for %s', field)
                self.log.info(content)
    def get_direct_relative_ids(self, upstream: bool = False) -> Set[str]:
        """
        Get set of the direct relative ids to the current task, upstream or
        downstream.
        """
        if upstream:
            return self._upstream_task_ids
        else:
            return self._downstream_task_ids
    def get_direct_relatives(self, upstream: bool = False) -> List["BaseOperator"]: