Update PyMemberDescrObject struct to match CPython (#5647)

* Update PyMemberDescrObject.d_member type

* Set for correct python versions

* Appease clippy and add news fragment

* Add conditional use

Author: SilasMarvin

newsfragments/5647.fixed.md

@@ -0,0 +1 @@
+Fix `PyMemberDescrObject.d_member` type in `pyo3-ffi` to use `PyMemberDef` for Python 3.11+ (was incorrectly `PyGetSetDef`).

pyo3-ffi/src/cpython/descrobject.rs

@@ -1,6 +1,9 @@
 use crate::{PyGetSetDef, PyMethodDef, PyObject, PyTypeObject};
 use std::ffi::{c_char, c_int, c_void};
 
+#[cfg(Py_3_11)]
+use crate::PyMemberDef;
+
 pub type wrapperfunc = Option<
     unsafe extern "C" fn(
         slf: *mut PyObject,
@@ -53,7 +56,10 @@ pub struct PyMethodDescrObject {
 #[repr(C)]
 pub struct PyMemberDescrObject {
     pub d_common: PyDescrObject,
+    #[cfg(not(Py_3_11))]
     pub d_member: *mut PyGetSetDef,
+    #[cfg(Py_3_11)]
+    pub d_member: *mut PyMemberDef,
 }
 
 #[repr(C)]