### 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/models/baseoperator.py
tr=weight_rule,
                )
            )
        self.weight_rule = weight_rule
        self.resources: Optional[Resources] = Resources(**resources) if resources else None
        self.run_as_user = run_as_user
        if task_concurrency and not max_active_tis_per_dag:
            
            warnings.warn(
                "The 'task_concurrency' parameter is deprecated. Please use 'max_active_tis_per_dag'.",
                DeprecationWarning,
                stacklevel=2,
            )
            max_active_tis_per_dag = task_concurrency
        self.max_active_tis_per_dag = max_active_tis_per_dag
        self.executor_config = executor_config or {}
        self.do_xcom_push = do_xcom_push
        self.doc_md = doc_md
        self.doc_json = doc_json
        self.doc_yaml = doc_yaml
        self.doc_rst = doc_rst
        self.doc = doc
        
        self._upstream_task_ids: Set[str] = set()
        self._downstream_task_ids: Set[str] = set()
        self._dag = None
        self.dag = dag or DagContext.get_current_dag()
        
        
        from airflow.models.dag import DAG