patch 9.1.0723: if_python: dynamic linking fails with python3 >= 3.13

patch 9.1.0723: if_python: dynamic linking fails with python3 >= 3.13

Problem:  if_python: dynamic linking fails with python3 >= 3.13
          when using non-stable ABI (zdohnal)
Solution: do not try to import the privat python symbol
          _PyObject_NextNotImplemented
          (Yee Cheng Chin)

Vim is importing a private Python symbol `_PyObject_NextNotImplemented`
because it used to be required as part of the `PyIter_Check()` macro in
an abstraction breaking way. Python eventually fixed the issue and in
3.13 it removed the private symbol export, which broke Vim. Simply
remove importing this private symbol in newer Python versions as it's no
longer needed for PyIter_Check to work.

fixes: #15457
closes: #15649

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>