The `OUTLINER_OT_item_activate` operator, although it detects when
something changes, always returns `OPERATOR_FINISHED` and thus induces
the creation of undo steps.
So return `OPERATOR_CANCELLED` when nothing changes.
Ref T94080
Reviewed By: Severin
Maniphest Tasks: T94080
Differential Revision: https://developer.blender.org/D13638
3775615aea