A possible simple fix is to change these lines https://github.com/python/cpython/blob/main/Objects/unionobject.c#L294-L301

to:
```
    return (
        is_typevar(obj) |
        is_new_type(obj) |
        is_special_form(obj) |
        PyType_Check(obj) |
        PyObject_TypeCheck(obj, &Py_GenericAliasType) |
        (int)(type == &_Py_UnionType));
```

However, that may slow down union a little since we lose the short-circuiting that `||` provides over `|`, and all checks have to be evaluated.

Checking each result individually and mimicking the short circuiting behavior works too, so I did that. What do you think Serhiy?