fix: fix folding

Signed-off-by: Sefa Eyeoglu <[e-mail]>

nix/modules/base/neovim/treesitter.nix

···
   flake.modules.nixos.base.programs.nixvim = {
     plugins.treesitter = {
       enable = true;
-      folding = false;
+      folding.enable = false;
       settings.indent.enable = true;
     };
   };