GNOME Shell 42 switched an icon for the accessibility menu in the top panel
to one from gnome-control-center instead of a legacy one from adwaita-icon-theme:
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2155
Let’s add that dependency to the systemd unit since installing it
through `environment.systemPackages` is not enough due to environment isolation.