Very simple fix for issue #8235

In solve_poly_inequality, the real roots of a polynomial are sorted. When the
roots are instances of RootOf, this will invoke bool() on an instance of
Relational, which raises a TypeError. One fix is to cast all the roots as
floats for comparison.

Fixes #8235
> unless a function implies [...] to return a different ordering

Why do you think it's not the case?

The bad news that Poly.all_roots in general return list neither in the canonical order (i.e. with default_sort_key), nor ordered by interval value.  https://github.com/sympy/sympy/pull/8256#issuecomment-59285335