### 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
if isinstance(arg, XComArg):
                self.set_upstream(arg.operator)
            elif isinstance(arg, (tuple, set, list)):
                for elem in arg:
                    apply_set_upstream(elem)
            elif isinstance(arg, dict):
                for elem in arg.values():
                    apply_set_upstream(elem)
            elif hasattr(arg, "template_fields"):
                for elem in arg.template_fields:
                    apply_set_upstream(elem)
        for field in self.template_fields:
            if hasattr(self, field):
                arg = getattr(self, field)
                apply_set_upstream(arg)
    @property
    def priority_weight_total(self) -> int:
        """
        Total priority weight for the task. It might include all upstream or downstream tasks.
        depending on the weight rule.
          - WeightRule.ABSOLUTE - only own weight
          - WeightRule.DOWNSTREAM - adds priority weight of all downstream tasks
          - WeightRule.UPSTREAM - adds priority weight of all upstream tasks
        """
        if self.weight_rule == WeightRule.ABSOLUTE:
            return self.priority_weight
        elif self.weight_rule == WeightRule.DOWNSTREAM:
            upstream = False
        elif self.weight_rule == WeightRule.UPSTREAM: