### 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)

],
    )
    def test_short_circuit_with_teardowns(
        self, dag_maker, ignore_downstream_trigger_rules, should_skip, with_teardown, expected
    ):
        with dag_maker() as dag:
            op1 = ShortCircuitOperator(
                task_id="op1",
                python_callable=lambda: not should_skip,
                ignore_downstream_trigger_rules=ignore_downstream_trigger_rules,
            )
            op2 = PythonOperator(task_id="op2", python_callable=print)
            op3 = PythonOperator(task_id="op3", python_callable=print)
            op4 = PythonOperator(task_id="op4", python_callable=print)
            if with_teardown:
                op4.as_teardown()
            op1 >> op2 >> op3 >> op4
            op1.skip = MagicMock()
            dagrun = dag_maker.create_dagrun()
            tis = dagrun.get_task_instances()
            ti: TaskInstance = [x for x in tis if x.task_id == "op1"][0]
            ti._run_raw_task()
            expected_tasks = {dag.task_dict[x] for x in expected}
        if should_skip:
            
            actual_skipped = set(op1.skip.call_args.kwargs["tasks"])
            assert actual_skipped == expected_tasks
        else:
            op1.skip.assert_not_called()
    @pytest.mark.parametrize("config", ["sequence", "parallel"])