Add an XFAIL

Author: asmeurer

array-api-tests-xfails.txt

@@ -13,3 +13,7 @@ array_api_tests/test_fft.py::test_rfftn
 array_api_tests/test_fft.py::test_irfftn
 array_api_tests/test_fft.py::test_hfft
 array_api_tests/test_fft.py::test_ihfft
+
+# Known special case issue in NumPy. Not worth working around here
+# https://github.com/numpy/numpy/issues/21213
+array_api_tests/test_special_cases.py::test_iop[__ipow__(x1_i is -infinity and x2_i > 0 and not (x2_i.is_integer() and x2_i % 2 == 1)) -> +infinity]