nixos/incus: avoid restart on switch for incus-startup (#444760)

nixos/modules/virtualisation/incus.nix

···
       requires = [ "incus.socket" ];
       wantedBy = config.systemd.services.incus.wantedBy;
 
+      # restarting this service will affect instances
+      restartIfChanged = false;
+
       serviceConfig = {
         ExecStart = "${incus-startup} start";
         ExecStop = "${incus-startup} stop";