### 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/serialization/serialized_objects.py
type_ = encoded_var[Encoding.TYPE]
        if type_ == DAT.DICT:
            return {k: cls._deserialize(v) for k, v in var.items()}
        elif type_ == DAT.DAG:
            return SerializedDAG.deserialize_dag(var)
        elif type_ == DAT.OP:
            return SerializedBaseOperator.deserialize_operator(var)
        elif type_ == DAT.DATETIME:
            return pendulum.from_timestamp(var)
        elif type_ == DAT.POD:
            if not HAS_KUBERNETES:
                raise RuntimeError("Cannot deserialize POD objects without kubernetes libraries installed!")
            pod = PodGenerator.deserialize_model_dict(var)
            return pod
        elif type_ == DAT.TIMEDELTA:
            return datetime.timedelta(seconds=var)
        elif type_ == DAT.TIMEZONE:
            return decode_timezone(var)
        elif type_ == DAT.RELATIVEDELTA:
            return decode_relativedelta(var)
        elif type_ == DAT.SET:
            return {cls._deserialize(v) for v in var}
        elif type_ == DAT.TUPLE:
            return tuple(cls._deserialize(v) for v in var)
        else:
            raise TypeError(f'Invalid type {type_!s} in deserialization.')
    _deserialize_datetime = pendulum.from_timestamp
    _deserialize_timezone = pendulum.tz.timezone
    @classmethod
    def _deserialize_timedelta(cls, seconds: int) -> datetime.timedelta: