### 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
return self.__dict__ == other.__dict__
        def __ne__(self, other):
            return not self.__eq__(other)
    @parameterized.expand(
        [
            (None, None),
            ([], []),
            ({}, {}),
            ("{{ task.task_id }}", "{{ task.task_id }}"),
            (["{{ task.task_id }}", "{{ task.task_id }}"]),
            ({"foo": "{{ task.task_id }}"}, {"foo": "{{ task.task_id }}"}),
            ({"foo": {"bar": "{{ task.task_id }}"}}, {"foo": {"bar": "{{ task.task_id }}"}}),
            (
                [{"foo1": {"bar": "{{ task.task_id }}"}}, {"foo2": {"bar": "{{ task.task_id }}"}}],
                [{"foo1": {"bar": "{{ task.task_id }}"}}, {"foo2": {"bar": "{{ task.task_id }}"}}],
            ),
            (
                {"foo": {"bar": {"{{ task.task_id }}": ["sar"]}}},
                {"foo": {"bar": {"{{ task.task_id }}": ["sar"]}}},
            ),
            (
                ClassWithCustomAttributes(
                    att1="{{ task.task_id }}", att2="{{ task.task_id }}", template_fields=["att1"]
                ),
                "ClassWithCustomAttributes("
                "{'att1': '{{ task.task_id }}', 'att2': '{{ task.task_id }}', 'template_fields': ['att1']})",
            ),
            (
                ClassWithCustomAttributes(