### 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)

tests/serialization/test_dag_serialization.py
"""Serialisation / deserialisation continues to work without kubernetes installed"""
    def mock__import__(name, globals_=None, locals_=None, fromlist=(), level=0):
        if level == 0 and name.partition('.')[0] == 'kubernetes':
            raise ImportError("No module named 'kubernetes'")
        return importlib.__import__(name, globals=globals_, locals=locals_, fromlist=fromlist, level=level)
    with mock.patch('builtins.__import__', side_effect=mock__import__) as import_mock:
        # load module from scratch, this does not replace any already imported
        # airflow.serialization.serialized_objects module in sys.modules
        spec = importlib.util.find_spec("airflow.serialization.serialized_objects")
        module = importlib.util.module_from_spec(spec)
        spec.loader.exec_module(module)
        # if we got this far, the module did not try to load kubernetes, but
        # did it try to access airflow.kubernetes.*?
        imported_airflow = {
            c.args[0].split('.', 2)[1] for c in import_mock.call_args_list if c.args[0].startswith("airflow.")
        }
        assert "kubernetes" not in imported_airflow
        # pod loading is not supported when kubernetes is not available
        pod_override = {
            '__type': 'k8s.V1Pod',
            '__var': PodGenerator.serialize_pod(executor_config_pod),
        }
        with pytest.raises(RuntimeError):
            module.BaseSerialization.from_dict(pod_override)
        # basic serialization should succeed
        module.SerializedDAG.to_dict(make_simple_dag()["simple_dag"])