[NVIM] Skip plugin update check on nvim < 0.10

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

nvim/init.vim

@@ -76,6 +76,10 @@ call plug#end()
 " Check for plugin updates after the editor is responsive.
 lua << EOF
 local function check_plugin_updates()
+    if vim.system == nil then
+        return -- needs nvim >= 0.10
+    end
+
     local plugins = {}
     for name, plugin in pairs(vim.g.plugs or {}) do
         if vim.fn.isdirectory(plugin.dir) == 1 then