Fix #105757: Resizing images is not marking them as changed

Resizing an image via the operator did not mark it dirty
(`IB_BITMAPDIRTY` is needed to pick this up as being modified, if this is
not set, no warning/option is shown on file close).

Note that using RNA would already do this correctly (since it uses
`BKE_image_scale` -- which already calls `BKE_image_mark_dirty`
internally).

Pull Request: blender/blender#105851

source/blender/editors/space_image/image_ops.c

@@ -3008,6 +3008,7 @@ static int image_scale_exec(bContext *C, wmOperator *op)
 
   ibuf->userflags |= IB_DISPLAY_BUFFER_INVALID;
   IMB_scaleImBuf(ibuf, size[0], size[1]);
+  BKE_image_mark_dirty(ima, ibuf);
   BKE_image_release_ibuf(ima, ibuf, NULL);
 
   ED_image_undo_push_end();