Py::new and .into_py are inconsistent on complex enums

Py::new and .into_py are currently inconsistent.
Note how the constructed value in the example below is not an instance of the specific variant.
This is intended to be fixed before 0.21, see review comment here:
https://github.com/PyO3/pyo3/pull/3582/files#r1451402473

use pyo3::prelude::*;

#[pyclass]
enum MyEnum {
    Variant { i: i32 },
}

Python::with_gil(|py| {
    let x = Py::new(py, MyEnum::Variant { i: 42 }).unwrap();
    let cls = py.get_type::<MyEnum>();
    pyo3::py_run!(py, x cls, r#"
        assert isinstance(x, cls)
        assert not isinstance(x, cls.Variant)
    "#)
})

Use the provided MyEnum example as the reproducer; compare the behavior of Py::new and .into_py for the enum variant, and read the linked review comment for the intended pre-0.21 behavior. Done means the constructed value matches the expected isinstance relationships in the example.