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: https://projects.blender.org/blender/blender/pulls/105851