### Apache Airflow version

2.3.0

### What happened

When using a `PythonVirtualenvOperator` it is checked if `virtualenv` is installed by 
`if not shutil.which("virtualenv"):`
https://github.com/apache/airflow/blob/a1679be85aa49c0d6a7ba2c31acb519a5bcdf594/airflow/operators/python.py#L398
Actually, this expression checks if `virtualenv` is on PATH. If Airflow is installed in a virtual environment itself and `virtualenv` is not installed in the environment the check might pass but `virtualenv` cannot be used as it is not present in the environment.

### What you think should happen instead

It should be checked if `virtualenv` is actually available in the environment.

```python
if importlib.util.find_spec("virtualenv") is None:
    raise AirflowException('PythonVirtualenvOperator requires virtualenv, please install it.')
```
https://stackoverflow.com/a/14050282

### How to reproduce

_No response_

### Operating System

Ubuntu 20.04

### Versions of Apache Airflow Providers

_No response_

### Deployment

Virtualenv installation

### Deployment details

_No response_

### Anything else

_No response_

### 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)

(["a", "b", "c"], True, TriggerRule.ALL_SUCCESS, all_success_states),
            
            
            (True, True, TriggerRule.ALL_DONE, all_success_states),
            
            
            (["a", "b", "c"], True, TriggerRule.ALL_DONE, all_success_states),
            
            
            (True, False, TriggerRule.ALL_SUCCESS, all_success_states),
            
            
            (["a", "b", "c"], False, TriggerRule.ALL_SUCCESS, all_success_states),
            
            
            (True, False, TriggerRule.ALL_DONE, all_success_states),
            
            
            (["a", "b", "c"], False, TriggerRule.ALL_DONE, all_success_states),
        ],
        ids=[
            "skip_ignore_with_default_trigger_rule_on_all_tasks",
            "skip_falsy_result_ignore_with_default_trigger_rule_on_all_tasks",
            "skip_ignore_respect_with_non-default_trigger_rule_on_single_task",
            "skip_falsy_result_ignore_respect_with_non-default_trigger_rule_on_single_task",
            "skip_respect_with_default_trigger_rule_all_tasks",
            "skip_falsy_result_respect_with_default_trigger_rule_all_tasks",
            "skip_respect_with_non-default_trigger_rule_on_single_task",
            "skip_falsy_result_respect_respect_with_non-default_trigger_rule_on_single_task",