wingpanel-indicator-ayatana: add passthru.updateScript

Upstream doesn't tag release, we use unstableGitUpdater.

pkgs/desktops/pantheon/third-party/wingpanel-indicator-ayatana/default.nix

@@ -1,6 +1,7 @@
 { lib
 , stdenv
 , fetchFromGitHub
+, unstableGitUpdater
 , substituteAll
 , meson
 , ninja
@@ -45,6 +46,12 @@ stdenv.mkDerivation rec {
     pantheon.wingpanel
   ];
 
+  passthru = {
+    updateScript = unstableGitUpdater {
+      url = "https://github.com/Lafydev/wingpanel-indicator-ayatana.git";
+    };
+  };
+
   meta = with lib; {
     description = "Ayatana Compatibility Indicator for Wingpanel";
     homepage = "https://github.com/Lafydev/wingpanel-indicator-ayatana";