gnunet: fix systemd service config (#151269)

Co-authored-by: Jörg Thalheim <[e-mail]>

nixos/modules/services/networking/gnunet.nix

···
       description = "GNUnet";
       after = [ "network.target" ];
       wantedBy = [ "multi-user.target" ];
-      restartTriggers = [ configFile ];
+      restartTriggers = [ config.environment.etc."gnunet.conf".source ];
       path = [ cfg.package pkgs.miniupnpc ];
       serviceConfig.ExecStart = "${cfg.package}/lib/gnunet/libexec/gnunet-service-arm -c /etc/gnunet.conf";
       serviceConfig.User = "gnunet";