Enable treesitter if no on nix, but disable auto_install

lua/plugins/treesitter.lua

@@ -1,6 +1,5 @@
 return {
     "nvim-treesitter/nvim-treesitter",
-    cond = function() return vim.fn.executable "nix" == 1 end,
     version = false,
     build = ":TSUpdate",
     event = { "BufReadPre", "BufNewFile" },
@@ -18,7 +17,7 @@ return {
         require("nvim-treesitter.configs").setup(opts)
     end,
     opts = {
-        auto_install = true,
+        auto_install = vim.fn.executable "nix" == 1,
         highlight = {
             enable = true,
             disable = { "fortran" },