### 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
(
                {
                    "staging_schema": [
                        {"key:": "foo", "value": "bar"},
                        {"key:": "this", "value": "that"},
                        "test_conf",
                    ]
                },
                {
                    "staging_schema": [
                        {"__type": "dict", "__var": {"key:": "foo", "value": "bar"}},
                        {
                            "__type": "dict",
                            "__var": {"key:": "this", "value": "that"},
                        },
                        "test_conf",
                    ]
                },
            ),
            (
                {"task3": "test3", "task2": "test2", "task1": "test1"},
                {"task1": "test1", "task2": "test2", "task3": "test3"},
            ),
            (
                ('task_1', 'task_5', 'task_2', 3, ["x", "y"]),
                ['task_1', 'task_5', 'task_2', 3, ["x", "y"]],
            ),
        ]
    )
    def test_serialized_objects_are_sorted(self, object_to_serialized, expected_output):