Add torch xfail

Author: asmeurer

torch-xfails.txt

@@ -183,6 +183,7 @@ array_api_tests/test_statistical_functions.py::test_var
 # The test suite is incorrectly checking sums that have loss of significance
 # (https://github.com/data-apis/array-api-tests/issues/168)
 array_api_tests/test_statistical_functions.py::test_sum
+array_api_tests/test_statistical_functions.py::test_prod
 
 # These functions do not yet support complex numbers
 array_api_tests/test_operators_and_elementwise_functions.py::test_sign