`test_special_cases` uses incorrect test case for `copysign` with NaN

[ndgrigorian]

The spec splits copysign behavior into x1_1 is not NaN cases and x1_i is NaN cases. The special cases parser doesn't handle this properly, leading to incorrect test case generation:

In [3]: import array_api_tests.test_special_cases as tsc

In [4]: copysign_cases = [p.values[-1] for p in tsc.binary_params if p.values[0] == "copysign"]

In [5]: copysign_cases
Out[5]:
[BinaryCase(<x2_i < 0 -> NaN>),
 BinaryCase(<x2_i is -0 -> NaN>),
 BinaryCase(<x2_i is +0 -> NaN>),
 BinaryCase(<x2_i > 0 -> NaN>)]

In [6]: py_nan = float("nan")

In [7]: copysign_cases[0].check_result(1.0, -1.0, -1.0)
Out[7]: False

In [8]: copysign_cases[0].check_result(1.0, -1.0, py_nan)
Out[8]: True

In [9]: copysign_cases[1].check_result(1.0, -0.0, -1.0)
Out[9]: False

In [10]: copysign_cases[1].check_result(1.0, -0.0, py_nan)
Out[10]: True

In [11]: copysign_cases[2].check_result(-1.0, +0.0, 1.0)
Out[11]: False

In [12]: copysign_cases[2].check_result(-1.0, +0.0, py_nan)
Out[12]: True

In [13]: copysign_cases[3].check_result(-1.0, +1.0, 1.0)
Out[13]: False

In [14]: copysign_cases[3].check_result(-1.0, +1.0, py_nan)
Out[14]: True

[asmeurer]

Fixed at data-apis/array-api#806