Fix flaky test_versions test

[gsilvestrin]

test_versions in test_dataset.py is flaky. Sometime it fails with:

python/tests/test_dataset.py::test_versions FAILED                       [  9%]

=================================== FAILURES ===================================
________________________________ test_versions _________________________________

tmp_path = PosixPath('/tmp/pytest-of-runner/pytest-0/test_versions0')

    def test_versions(tmp_path: Path):
        table1 = pa.Table.from_pylist([{"a": 1, "b": 2}, {"a": 10, "b": 20}])
        base_dir = tmp_path / "test"
        lance.write_dataset(table1, base_dir)
    
        assert len(lance.dataset(base_dir).versions()) == 1
    
        table2 = pa.Table.from_pylist([{"s": "one"}, {"s": "two"}])
        time.sleep(1)
        lance.write_dataset(table2, base_dir, mode="overwrite")
    
        assert len(lance.dataset(base_dir).versions()) == 2
    
        v2, v1 = lance.dataset(base_dir).versions()
        assert isinstance(v1["timestamp"], datetime)
        assert isinstance(v2["timestamp"], datetime)
>       assert v1["timestamp"] < v2["timestamp"]
E       assert datetime.datetime(2023, 3, 8, 19, 2, 50, 956316) < datetime.datetime(2023, 3, 8, 19, 2, 49, 947502)

python/tests/test_dataset.py:58: AssertionError
============================= slowest 30 durations =============================

Look into why this happens. It is possible that we need to add an explicit sort on version number before returning in Rust to return versions in ascending order.