COMPAT: TestUnique.test_first_nan_kept failed for Python 3.10.0b1
```
________________________ TestUnique.test_first_nan_kept ________________________

self = <pandas.tests.test_algos.TestUnique object at 0x7efe1274c760>

    def test_first_nan_kept(self):
        # GH 22295
        # create different nans from bit-patterns:
        bits_for_nan1 = 0xFFF8000000000001
        bits_for_nan2 = 0x7FF8000000000001
        NAN1 = struct.unpack("d", struct.pack("=Q", bits_for_nan1))[0]
        NAN2 = struct.unpack("d", struct.pack("=Q", bits_for_nan2))[0]
        assert NAN1 != NAN1
        assert NAN2 != NAN2
        for el_type in [np.float64, object]:
            a = np.array([NAN1, NAN2], dtype=el_type)
            result = pd.unique(a)
>           assert result.size == 1
E           assert 2 == 1
E            +  where 2 = array([nan, nan], dtype=object).size

pandas/tests/test_algos.py:798: AssertionError
```

Note: I cannot reproduce it on M1 mac.