### 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
up_task_list = up_task
        down_task_list = down_task
        if len(up_task_list) != len(down_task_list):
            raise AirflowException(
                f'Chain not supported for different length Iterable. '
                f'Got {len(up_task_list)} and {len(down_task_list)}.'
            )
        for up_t, down_t in zip(up_task_list, down_task_list):
            up_t.set_downstream(down_t)
def cross_downstream(
    from_tasks: Sequence[Union[BaseOperator, "XComArg"]],
    to_tasks: Union[BaseOperator, "XComArg", Sequence[Union[BaseOperator, "XComArg"]]],
):
    r"""
    Set downstream dependencies for all tasks in from_tasks to all tasks in to_tasks.
    Using classic operators/sensors:
    .. code-block:: python
        cross_downstream(from_tasks=[t1, t2, t3], to_tasks=[t4, t5, t6])
    is equivalent to::
        t1 ---> t4
           \ /
        t2 -X -> t5
           / \
        t3 ---> t6
    .. code-block:: python
        t1.set_downstream(t4)
        t1.set_downstream(t5)
        t1.set_downstream(t6)
        t2.set_downstream(t4)
        t2.set_downstream(t5)