Avoid possible infinite recursion

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/user/configs/gui/ags/default.nix

@@ -1,5 +1,5 @@
 {
-  user ? throw "user argument is required",
+  username ? throw "username argument is required",
 }:
 {
   config,
@@ -9,11 +9,11 @@
   ...
 }:
 let
-  hmConfig = config.home-manager.users.${user.name};
+  hmConfig = config.home-manager.users.${username};
   agsConfig = import ./config { inherit pkgs; };
 in
 {
-  home-manager.users.${user.name} = {
+  home-manager.users.${username} = {
     imports = [ inputs.ags.homeManagerModules.default ];
 
     programs.ags.enable = true;