### 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,
        start_date: Optional[datetime] = None,
        end_date: Optional[datetime] = None,
        session: Session = None,
    ) -> List[TaskInstance]:
        """
        Get a set of task instance related to this task for a specific date
        range.
        """
        end_date = end_date or timezone.utcnow()
        return (
            session.query(TaskInstance)
            .filter(TaskInstance.dag_id == self.dag_id)
            .filter(TaskInstance.task_id == self.task_id)
            .filter(TaskInstance.execution_date >= start_date)
            .filter(TaskInstance.execution_date <= end_date)
            .order_by(TaskInstance.execution_date)
            .all()
        )
    def get_flat_relative_ids(