wlsunset: migrate to lib.cli.toCommandLineShellGNU

Migrates from the deprecated toGNUCommandLineShell to toCommandLineShellGNU.

This changes the output format from space-separated short options
(-t 3500) to concatenated GNU-style options (-t3500). Both formats
were verified to work correctly with wlsunset.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/services/wlsunset.nix

@@ -134,7 +134,7 @@ in
       Service = {
         ExecStart =
           let
-            args = lib.cli.toGNUCommandLineShell { } {
+            args = lib.cli.toCommandLineShellGNU { } {
               t = cfg.temperature.night;
               T = cfg.temperature.day;
               g = cfg.gamma;

tests/modules/services/wlsunset/wlsunset-service-expected.service

@@ -2,7 +2,7 @@
 WantedBy=test.target
 
 [Service]
-ExecStart=@wlsunset@/bin/wlsunset -L 128.8 -T 6000 -g 0.6 -l 12.3 -t 3500
+ExecStart=@wlsunset@/bin/wlsunset -L128.8 -T6000 -g0.6 -l12.3 -t3500
 
 [Unit]
 After=test.target