Fix transient bug in test with array_equal of empty arrays

[tbennun]

In some specific random seeds, the following error occurs:

tests/numpy/ufunc_support_test.py:130: in test_ufunc_add_where
    assert (not np.array_equal((A + B)[np.logical_not(W)], C[np.logical_not(W)]))
E   assert not True
E    +  where True = <function array_equal at 0x7f64de13d730>(array([], dtype=int32), array([], dtype=int32))
E    +    where <function array_equal at 0x7f64de13d730> = np.array_equal

This PR patches it by freezing the random seed.