environment.profiles: fix order of profiles

This change is needed because the order of profiles correlate to the
order in PATH, therefore "/etc/profiles/per-user/$USER" always appeared
after the system packages directories.

(cherry picked from commit 33c834f2fb2c25f2351cd0ae9b8cc361e033141b)

nixos/modules/config/users-groups.nix

···
       };
     }) (filterAttrs (_: u: u.packages != []) cfg.users));
 
-    environment.profiles = [ "/etc/profiles/per-user/$USER" ];
+    environment.profiles = [
+      "$HOME/.nix-profile"
+      "/etc/profiles/per-user/$USER"
+    ];
 
     assertions = [
       { assertion = !cfg.enforceIdUniqueness || (uidsAreUnique && gidsAreUnique);

nixos/modules/programs/environment.nix

···
         XCURSOR_PATH = [ "$HOME/.icons" ];
       };
 
-    environment.profiles =
-      [ "$HOME/.nix-profile"
-        "/nix/var/nix/profiles/default"
+    environment.profiles = mkAfter
+      [ "/nix/var/nix/profiles/default"
         "/run/current-system/sw"
       ];