Use gtk4-update-icon-cache instead of gtk3 one
I'm a maintainer for Helvum in Nixpkgs, and while updating to 0.3.2 (and also switching to meson, a bit late), I've found I needed to also include gtk3
in the dependencies, in order for the build to succeed calling gtk-update-icon-cache
. I was instructed here to fix this issue upstream if possible.