patch 9.1.1189: if_python: build error due to incompatible pointer types

patch 9.1.1189: if_python: build error due to incompatible pointer types

Problem:  if_python: build error due to incompatible pointer types
Solution: cast pointer to PyObject* (oreo639)

Avoid build failure due to -Wincompatible-pointer-types becoming an error in
gcc 14.
When Py_LIMITED_API is < 0x030b0000, then the for Py_XDECREF must be PyObject*.
Vim targets Py_LIMITED_API = 0x03080000 (python 3.8).

closes: #16824

Signed-off-by: oreo639 <oreo6391@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>