Treesitter doesn't seem to change its parse tree when changing
restriction. It gets it correct the first time when we query the root
node, but then, after changing restriction, it doesn't seem to get
updated.

The following is an M-x ielm session to demonstrate the problem

  ELISP> (set-buffer (get-buffer-create "test"))
  ELISP> (insert "echo '123'")
  ELISP> (narrow-to-region 1 4)
  ELISP> (buffer-string)
  "echo"
  ELISP> (treesit-buffer-root-node 'bash)
  #<treesit-node
  (program)
  in 1-4>  ;; This is expected

  ELISP> (widen)
  ELISP> (treesit-buffer-root-node 'bash)
  #<treesit-node
  (program)
  in 1-4>  ;; <---- This is not expected, the root node should span 1-9

  ELISP> (buffer-string)
  "echo '123'"