## Summary
It's only safe to enforce the `x in "1234567890"` case if `x` is exactly
one character, since the set on the right has been reordered as compared
to `string.digits`. We can't know if `x` is exactly one character unless
it's a literal. And if it's a literal, well, it's kind of silly code in
the first place?
Closes https://github.com/astral-sh/ruff/issues/13802.