Assembly: Fix unconnected Joints always touched

Fix https://github.com/FreeCAD/FreeCAD/issues/22642

src/Mod/Assembly/App/AssemblyObject.cpp

@@ -541,6 +541,7 @@ void AssemblyObject::recomputeJointPlacements(std::vector<App::DocumentObject*>
             Py::Tuple args(1);
             args.setItem(0, Py::asObject(joint->getPyObject()));
             Py::Callable(attr).apply(args);
+            joint->purgeTouched();
         }
     }
 }