Unnecessary parentheses when fix PLC2801

`ruff check a.py --select PLC2801 --fix --preview --unsafe-fixes` changes the code from
```python
assert 'kk'.__str__() == 'kk'
```
to
```python
assert (str('kk')) == 'kk'
```

expected behavior: `assert str('kk') == 'kk'`

My ruff version is 0.8.0