Improve the treesit check around expreg

Part of testing with Emacs 28

.gitignore

@@ -12,3 +12,4 @@ ielm-history.eld
 multisession/
 .cask/
 org-clock-save.el
+tramp

unravel-emacs.org

@@ -1216,7 +1216,8 @@ I expect ~expreg~ to eventually completely replace ~easy-kill~ ()
 
 #+begin_src emacs-lisp :tangle "unravel-modules/unravel-essentials.el"
   ;;; Mark syntactic constructs efficiently if tree-sitter is available (expreg)
-  (when (treesit-available-p)
+  (when (and (fboundp 'treesit-available-p)
+             (treesit-available-p))
     (use-package expreg
       :ensure t
       :functions (prot/expreg-expand prot/expreg-expand-dwim)

unravel-modules/unravel-essentials.el

@@ -103,7 +103,8 @@
   ("M-w" . easy-kill)) ; re-map kill-ring-save
 
 ;;; Mark syntactic constructs efficiently if tree-sitter is available (expreg)
-(when (treesit-available-p)
+(when (and (fboundp 'treesit-available-p)
+           (treesit-available-p))
   (use-package expreg
     :ensure t
     :functions (prot/expreg-expand prot/expreg-expand-dwim)