wayland/buffer: Pass g_object_unref to g_ptr_array_new_with_free_func
requested to merge daenzer/mutter:wayland-buffer-g_ptr_array_new_with_free_func-g_object_unref into main
The release_points array holds pointers to MetaWaylandSyncPoint objects.
Fixes leaking references (and ultimately the underlying memory) for the array elements.
Closes: #3442 (closed) Fixes: e8b890ab ("wayland: Implement linux-drm-syncobj-v1")