bpo-44339: Fix math.pow corner case to comply with IEEE 754 (GH-26606)

Change the behaviour of `math.pow(0.0, -math.inf)` and `math.pow(-0.0, -math.inf)` to return positive infinity instead of raising `ValueError`. This makes `math.pow` consistent with the built-in `pow` (and the `**` operator) for this particular special case, and brings the `math.pow` special-case handling into compliance with IEEE 754.

Modules/mathmodule.c

@@ -2810,8 +2810,6 @@ math_pow_impl(PyObject *module, double x, double y)
                 r = y;
             else if (y < 0. && fabs(x) < 1.0) {
                 r = -y; /* result is +inf */
-                if (x == 0.) /* 0**-inf: divide-by-zero */
-                    errno = EDOM;
             }
             else
                 r = 0.;