### 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)

tests/serialization/test_dag_serialization.py
"""
        Tests serialize_task_group, make sure the list is in order
        """
        from airflow.operators.dummy import DummyOperator
        from airflow.serialization.serialized_objects import SerializedTaskGroup
        from airflow.utils.task_group import TaskGroup
        """
                    start
                    ╱  ╲
                  ╱      ╲
        task_group_up1  task_group_up2
            (task_up1)  (task_up2)
                 ╲       ╱
              task_group_middle
                (task_middle)
                  ╱      ╲
        task_group_down1 task_group_down2
           (task_down1) (task_down2)
                 ╲        ╱
                   ╲    ╱
                    end
        """
        execution_date = datetime(2020, 1, 1)
        with DAG(dag_id="test_task_group_sorted", start_date=execution_date) as dag:
            start = DummyOperator(task_id="start")
            with TaskGroup("task_group_up1") as task_group_up1:
                _ = DummyOperator(task_id="task_up1")
            with TaskGroup("task_group_up2") as task_group_up2:
                _ = DummyOperator(task_id="task_up2")