### 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
"""Detects dependencies caused by tasks"""
        if task.task_type == "TriggerDagRunOperator":
            return DagDependency(
                source=task.dag_id,
                target=getattr(task, "trigger_dag_id"),
                dependency_type="trigger",
                dependency_id=task.task_id,
            )
        elif task.task_type == "ExternalTaskSensor":
            return DagDependency(
                source=getattr(task, "external_dag_id"),
                target=task.dag_id,
                dependency_type="sensor",
                dependency_id=task.task_id,
            )
        return None
class SerializedBaseOperator(BaseOperator, BaseSerialization):
    """A JSON serializable representation of operator.
    All operators are casted to SerializedBaseOperator after deserialization.
    Class specific attributes used by UI are move to object attributes.
    """
    _decorated_fields = {'executor_config'}
    _CONSTRUCTOR_PARAMS = {
        k: v.default
        for k, v in signature(BaseOperator.__init__).parameters.items()
        if v.default is not v.empty
    }
    dependency_detector = conf.getimport('scheduler', 'dependency_detector')
    def __init__(self, *args, **kwargs):