gh-111178: Avoid calling functions from incompatible pointer types in listobject.c (GH-112820)

Fix undefined behavior warnings (UBSan  -fsanitize=function), for example:

Objects/object.c:674:11: runtime error: call to function list_repr through pointer to incorrect function type 'struct _object *(*)(struct _object *)'
listobject.c:382: note: list_repr defined here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior Objects/object.c:674:11 in