Use of deprecated function PyEval_CallObject breaks build of Python wrapper on Python 3.13

[h4vismat]

The current implementation of swig_green_gdk.i for the Python SWIG calls PyEval_CallObject(), which has been deprecated since Python 3.9. This effectively breaks the build for the Python wrapper, as these functions are not defined anymore in Python 3.13. To keep up with the current CPython implementation, this needs to be addressed.

 3359 |     handler = PyEval_CallObject(handler_ref, NULL);
      |               ^
swig_green_gdk_wrap.c:3359:13: error: incompatible integer to pointer conversion assigning to 'PyObject *' (aka 'struct _object *') from 'int' [-Wint-conversion]
 3359 |     handler = PyEval_CallObject(handler_ref, NULL);
      |             ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
swig_green_gdk_wrap.c:3369:13: error: incompatible integer to pointer conversion assigning to 'PyObject *' (aka 'struct _object *') from 'int' [-Wint-conversion]
 3369 |         ret = PyEval_CallObject(handler, args);
      |             ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3 errors generated.
error: command '/usr/bin/clang' failed with exit code 1

ERROR Backend subprocess exited when trying to invoke build_wheel
make[3]: *** [src/swig_python/python-wheel-canary-file] Error 1
make[2]: *** [src/swig_python/CMakeFiles/python-wheel.dir/all] Error 2
make[1]: *** [src/swig_python/CMakeFiles/python-wheel.dir/rule] Error 2
make: *** [python-wheel] Error 2

After Python 3.9, the correct function to be used is PyObject_CallObject(), as defined on the Python 3.9 what's new page, and on the following CPython PR.

[h4vismat]

I have already implemented a fix on the following PR: #215
Feel free to point out any considerations.

[jgriffiths]

Fixed in master, thanks.