Attacher: fix wrong superPlacement read-onlyness
Attacher: fix wrong superPlacement read-onlyness

It reacted to changes to unrelated properties. Fixed.

maurerpe/FreeCAD,usakhelo/FreeCAD,bblacey/FreeCAD-MacOS-CI,bblacey/FreeCAD-MacOS-CI,timthelion/FreeCAD,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,chrisjaquet/FreeCAD,maurerpe/FreeCAD,chrisjaquet/FreeCAD,bblacey/FreeCAD-MacOS-CI,wood-galaxy/FreeCAD,wood-galaxy/FreeCAD,bblacey/FreeCAD-MacOS-CI,chrisjaquet/FreeCAD,timthelion/FreeCAD,usakhelo/FreeCAD,usakhelo/FreeCAD,bblacey/FreeCAD-MacOS-CI,timthelion/FreeCAD,usakhelo/FreeCAD,chrisjaquet/FreeCAD,chrisjaquet/FreeCAD,chrisjaquet/FreeCAD,chrisjaquet/FreeCAD,wood-galaxy/FreeCAD,timthelion/FreeCAD,timthelion/FreeCAD,bblacey/FreeCAD-MacOS-CI,usakhelo/FreeCAD,usakhelo/FreeCAD,wood-galaxy/FreeCAD,bblacey/FreeCAD-MacOS-CI,maurerpe/FreeCAD,timthelion/FreeCAD,maurerpe/FreeCAD,usakhelo/FreeCAD,Fat-Zer/FreeCAD_sf_master,wood-galaxy/FreeCAD,wood-galaxy/FreeCAD,maurerpe/FreeCAD,Fat-Zer/FreeCAD_sf_master