Fix #119508: Missing update after "Shade Flat" operator

An alternative fix would be calling `update_on_change_` in the
attribute `try_create`function, but sticking with this more
conservative fix seems better for 4.1.

Pull Request: https://projects.blender.org/blender/blender/pulls/119515

source/blender/editors/object/object_edit.cc

@@ -1612,6 +1612,7 @@ static int shade_smooth_exec(bContext *C, wmOperator *op)
         const float angle = RNA_float_get(op->ptr, "angle");
         bke::mesh_sharp_edges_set_from_angle(mesh, angle, keep_sharp_edges);
       }
+      mesh.tag_sharpness_changed();
       BKE_mesh_batch_cache_dirty_tag(static_cast<Mesh *>(ob->data), BKE_MESH_BATCH_DIRTY_ALL);
       changed = true;
     }