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
> all polyroots functions sort consistently with default_sort_key

Actually, this is not true (e.g. roots_cubic uses sorted).

> My position: all_roots is a rootoftools function and roots_quadratic is a polyroots function.

Both from the same module.

> We should not expect them to behave the same

Why not?

> especially when RootOf instances can't be sorted according to an expression.

What you mean?  We *can* use default_sort_key here as well:
```python
In [7]: list(ordered(Poly(x**2 - 2).all_roots(radicals=False), keys=default_sort_key))
Out[7]: 
⎡      ⎛ 2       ⎞        ⎛ 2       ⎞⎤
⎣RootOf⎝x  - 2, 0⎠, RootOf⎝x  - 2, 1⎠⎦
```