nixos/vim: assert that both enable and defaultEditor is set

nixos/modules/programs/vim.nix

@@ -17,10 +17,12 @@ in
     package = lib.mkPackageOption pkgs "vim" { example = [ "vim-full" ]; };
   };
 
-  # TODO: convert it into assert after 24.11 release
   config = lib.mkIf (cfg.enable || cfg.defaultEditor) {
-    warnings = lib.mkIf (cfg.defaultEditor && !cfg.enable) [
-      "programs.vim.defaultEditor will only work if programs.vim.enable is enabled, which will be enforced after the 24.11 release"
+    assertions = [
+      {
+        assertion = cfg.defaultEditor -> cfg.enable;
+        message = "{option}`programs.vim.defaultEditor` requires {option}`programs.vim.enable` to be set to true.";
+      }
     ];
     environment = {
       systemPackages = [ cfg.package ];