[`refurb`] Mark `FURB180` fix unsafe when class has bases (#18149)
<!--
Thank you for contributing to Ruff/ty! To help us out with reviewing,
please consider the following:
- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title? (Please prefix
with `[ty]` for ty pull
requests.)
- Does this pull request include references to any relevant issues?
-->
## Summary
Mark `FURB180`'s fix as unsafe if the class already has base classes.
This is because the base classes might validate the other base classes
(like `typing.Protocol` does) or otherwise alter runtime behavior if
more base classes are added.
## Test Plan
The existing snapshot test covers this case already.
## References
Partially addresses https://github.com/astral-sh/ruff/issues/13307 (left
out way to permit certain exceptions)
---------
Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>
Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
