gossip: add copyDesktopItems mimeTypes

pkgs/by-name/go/gossip/package.nix

···
   libGL,
   libxkbcommon,
   makeDesktopItem,
+  copyDesktopItems,
   openssl,
   pkg-config,
   rustPlatform,
···
     git
     pkg-config
     rustPlatform.bindgenHook
+    copyDesktopItems
   ]
   ++ lib.optionals stdenv.hostPlatform.isLinux [
     wayland-scanner
···
         "InstantMessaging"
       ];
       startupWMClass = "gossip";
+      mimeTypes = [ "x-scheme-handler/nostr" ];
     })
   ];