### 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
"""A serialized DAG can be deserialized in another process."""
        
        
        
        queue = multiprocessing.Queue()
        proc = multiprocessing.Process(target=serialize_subprocess, args=(queue, "airflow/example_dags"))
        proc.daemon = True
        proc.start()
        stringified_dags = {}
        while True:
            v = queue.get()
            if v is None:
                break
            dag = SerializedDAG.from_json(v)
            assert isinstance(dag, DAG)
            stringified_dags[dag.dag_id] = dag
        dags = collect_dags("airflow/example_dags")
        assert set(stringified_dags.keys()) == set(dags.keys())
        
        for dag_id in stringified_dags:
            self.validate_deserialized_dag(stringified_dags[dag_id], dags[dag_id])
    def test_roundtrip_provider_example_dags(self):