### 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
.. code-block:: python
        cross_downstream(from_tasks=[t1, x2(), t3], to_tasks=[x1(), t2, x3()])
    is equivalent to::
        t1 ---> x1
           \ /
        x2 -X -> t2
           / \
        t3 ---> x3
    .. code-block:: python
        x1 = x1()
        x2 = x2()
        x3 = x3()
        t1.set_downstream(x1)
        t1.set_downstream(t2)
        t1.set_downstream(x3)
        x2.set_downstream(x1)
        x2.set_downstream(t2)
        x2.set_downstream(x3)
        t3.set_downstream(x1)
        t3.set_downstream(t2)
        t3.set_downstream(x3)
    :param from_tasks: List of tasks or XComArgs to start from.
    :type from_tasks: List[airflow.models.BaseOperator] or List[airflow.models.XComArg]
    :param to_tasks: List of tasks or XComArgs to set as downstream dependencies.
    :type to_tasks: List[airflow.models.BaseOperator] or List[airflow.models.XComArg]
    """
    for task in from_tasks:
        task.set_downstream(to_tasks)
@attr.s(auto_attribs=True)
class BaseOperatorLink(metaclass=ABCMeta):