fix(lsp-format-buffer-on-save): :safe syntax to correctly (#4761)

My
[feat: `lsp-format-buffer-on-save` configurable via `.dir-locals.el` by ncaq · Pull Request #4760 · emacs-lsp/lsp-mode](#4760)
is invalid.
I fix to `:safe #'booleanp` syntax.

Author: ncaq

Diff for: lsp-mode.el

@@ -579,7 +579,7 @@ before saving a document."
   "If non-nil format buffer on save.
 To only format specific major-mode buffers see `lsp-format-buffer-on-save-list'."
   :type 'boolean
-  :safe t
+  :safe #'booleanp
   :local t
   :group 'lsp-mode)