Add a missing NumPy 1.21 xfail

Author: asmeurer

numpy-1-21-xfails.txt

@@ -112,6 +112,7 @@ array_api_tests/test_operators_and_elementwise_functions.py::test_floor_divide[_
 array_api_tests/test_operators_and_elementwise_functions.py::test_floor_divide[__floordiv__(x1, x2)]
 array_api_tests/test_operators_and_elementwise_functions.py::test_floor_divide[__ifloordiv__(x, s)]
 array_api_tests/test_operators_and_elementwise_functions.py::test_floor_divide[floor_divide(x1, x2)]
+array_api_tests/test_operators_and_elementwise_functions.py::test_greater[greater(x1, x2)]
 array_api_tests/test_operators_and_elementwise_functions.py::test_logaddexp
 array_api_tests/test_operators_and_elementwise_functions.py::test_multiply[__imul__(x, s)]
 array_api_tests/test_operators_and_elementwise_functions.py::test_multiply[__mul__(x, s)]