nixos/redmine: Fix misleading Ruby version number

Since commit 2f42412f78 ("ruby_3_2: drop") the example snippet for the
option `services.redmine.package` uses an unsupported Ruby version now.
Change it to Ruby 3.3, which is supported.

Signed-off-by: Felix Singer <felixsinger@posteo.net>

nixos/modules/services/misc/redmine.nix

@@ -80,7 +80,7 @@ in
       enable = lib.mkEnableOption "Redmine, a project management web application";
 
       package = lib.mkPackageOption pkgs "redmine" {
-        example = "redmine.override { ruby = pkgs.ruby_3_4; }";
+        example = "redmine.override { ruby = pkgs.ruby_3_3; }";
       };
 
       user = lib.mkOption {