[3.12] gh-123836: Check zero signs in math_testcases.txt (GH-123854) (#124162)

gh-123836: Check zero signs in math_testcases.txt (GH-123854)

Just like cmath_testcases.txt. These tests require IEEE 754 anyway.

Correct zero sign for sqrt tests to match math.h convention.
(cherry picked from commit 28aea5d07d163105b42acd81c1651397ef95ea57)

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>