modules/gickup: run linktree after gickup fetches are done

modules/gickup/update-linktree.nix

@@ -16,6 +16,8 @@ in
 
     # TODO: update symlink for one repo at a time (e.g. gickup-linktree@<instance>.service)
     systemd.services."gickup-linktree" = {
+      after = map ({ slug, ... }: "gickup@${slug}.service") (lib.attrValues cfg.instances)
+      wantedBy = [ "gickup.target" ];
       serviceConfig = {
         Type = "oneshot";
         ExecStart = let