gnome 45: Fix build error due to invalid pointer types with cast
Fixes build with -Wincompatible-pointer-types.
Not sure if this is because I am building in a Fedora 40 toolbox, but these warnings actually yield errors, making the build not work. The same for the CI currently (https://gitlab.gnome.org/velsinki/gnome-control-center/-/jobs/3516368).
Edited by Matthijs Velsink