### 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
op.operator_extra_links
            )
        if op.deps is not BaseOperator.deps:
            
            
            
            deps = []
            for dep in op.deps:
                klass = type(dep)
                module_name = klass.__module__
                if not module_name.startswith("airflow.ti_deps.deps."):
                    raise SerializationError(
                        f"Cannot serialize {(op.dag.dag_id + '.' + op.task_id)!r} with `deps` from non-core "
                        f"module {module_name!r}"
                    )
                deps.append(f'{module_name}.{klass.__name__}')
            
            
            
            serialize_op['deps'] = sorted(deps)
        
        
        if op.template_fields:
            for template_field in op.template_fields:
                value = getattr(op, template_field, None)
                if not cls._is_excluded(value, template_field, op):
                    serialize_op[template_field] = serialize_template_field(value)
        return serialize_op
    @classmethod
    def deserialize_operator(cls, encoded_op: Dict[str, Any]) -> BaseOperator: