redshift/gammastep: fix tray.target dependency

Fix a missing dependency for `tray.target` in `redshift/gammastep` module when the tray feature is enabled.

This caused a race condition that could result in the redshift/gammastep systemd user unit failing because the tray provider (e.g. waybar) isn't ready yet.

Author: evyatark2

modules/services/redshift-gammastep/lib/options.nix

@@ -189,8 +189,10 @@ in {
       in {
         Description = "${programName} colour temperature adjuster";
         Documentation = serviceDocumentation;
-        After = [ "graphical-session.target" ] ++ geoclueAgentService;
+        After = [ "graphical-session.target" ]
+          ++ (lib.optional cfg.tray "tray.target") ++ geoclueAgentService;
         Wants = geoclueAgentService;
+        Requires = lib.mkIf cfg.tray "tray.target";
         PartOf = [ "graphical-session.target" ];
       };