fix(health): normalize both sides of runtimepath comparison

The health check was incorrectly reporting "ERROR is not in runtimepath"
because it compared the install directory (without trailing slash) against
runtimepath entries with a trailing slash added. This caused false positives
even when the directory was correctly in runtimepath.

Fix by normalizing both paths consistently before comparison.

lua/nvim-treesitter/health.lua

@@ -97,7 +97,7 @@ local function install_health()
   end
   if
     vim.iter(vim.api.nvim_list_runtime_paths()):any(function(p)
-      return installdir == vim.fs.normalize(p) .. '/'
+      return vim.fs.normalize(installdir) == vim.fs.normalize(p)
     end)
   then
     health.ok('is in runtimepath.')