[tree-sitter][ts-fold] fix global mode activation

New version of ts-fold breaks in modes in which tree-sitter isn't supported.
Based on
[this](emacs-tree-sitter/ts-fold#121 (comment))
issue and comment, update the ts-fold activation for major mode.

layers/+tools/tree-sitter/packages.el

@@ -56,5 +56,6 @@
       (if tree-sitter-fold-indicators-enable
           (progn
             (setq ts-fold-indicators-priority 0)
-            (global-ts-fold-indicators-mode))
+            (add-hook 'tree-sitter-after-on-hook #'ts-fold-indicators-mode)
+            )
         (global-ts-fold-mode)))))