Fix for RUF023 should be unsafe because slot order can matter

[dscorbett]

The fix for RUF023 should be marked unsafe because the order of slots can be intentionally relied on, and changing it can change behavior. The fix is still safe if __slots__ is declared as a set.

$ ruff --version
ruff 0.5.6
$ cat ruf023.py 
class Fraction:
    __slots__ = "numerator", "denominator"

    __match_args__ = __slots__

    def __init__(self, numerator, denominator):
        self.numerator = numerator
        self.denominator = denominator


match Fraction(1, 2):
    case Fraction(1, 2):
        print("matched")
    case _:
        print("not matched")
$ python ruf023.py
matched
$ ruff check --isolated --preview --select RUF023 ruf023.py --fix
Found 1 error (1 fixed, 0 remaining).
$ python ruf023.py
not matched