org-element: Raise gc-cons-threshold for org-element-cache-map

This garbage collects many times when calling
`org-get-buffer-tags' (such as during tag completion) in a large file
with many tags.  Raise `gc-cons-threshold' as this may affect other
callers in large files.

Note that `org-element-parse-buffer' also raises `gc-cons-threshold'
as a precedent.

This has no effect on most callers and increases performance for
extreme cases.

* lisp/org-element.el (org-element-cache-map): Raise
`gc-cons-threshold'.

lisp/org-element.el

@@ -7577,7 +7577,8 @@ the cache."
       (let ((mk (make-marker)))
         (set-marker mk to-pos)
         (setq to-pos mk)))
-    (let (;; Bind variables used inside loop to avoid memory
+    (let ((gc-cons-threshold #x40000000)
+          ;; Bind variables used inside loop to avoid memory
           ;; re-allocation on every iteration.
           ;; See https://emacsconf.org/2021/talks/faster/
           tmpnext-start tmpparent tmpelement)