S603: `sys.executable` flagged as untrusted input

### Summary

Ruff treats `sys.executable` as untrusted input when AFAIK it is not.

```py
subprocess.run([sys.executable, "-m", "pip", "install", "ruff"], check=True)
```

In Ruff 0.15.6, this gets flagged with ``S603 `subprocess` call: check for execution of untrusted input``.

#17112 was solved by allowing string literals, so maybe another exception can be added?