PyAPI: don't use deprecated PyModule_GetFilename

Allows compiling with newer Python versions.
Also add missing decref when compiling as a py-module.

source/blender/python/intern/bpy_interface.c

@@ -869,6 +869,7 @@ static void bpy_module_delay_init(PyObject *bpy_proxy)
 
 	BLI_strncpy(filename_abs, filename_rel, sizeof(filename_abs));
 	BLI_path_cwd(filename_abs, sizeof(filename_abs));
+	Py_DECREF(filename_obj);
 
 	argv[0] = filename_abs;
 	argv[1] = NULL;