Tidy: Use alternatives to map-put

Emacs 27 marks map-put as obsolete and renames it to map-put!, which
causes byte-compilation warnings (sigh...isn't that the definition of
useless churn?).  Of course, map-put! doesn't exist in Emacs 26, so we
can't just use that.  I'm beginning to think that it will never be
possible to make the linting clean.

org-ql.el

@@ -477,7 +477,7 @@ Values compared with `equal'."
                (puthash (current-buffer)
                         (cons (buffer-modified-tick) position-cache)
                         org-ql-node-value-cache))
-             (map-put value-cache fn new-value)
+             (setf (alist-get fn value-cache nil nil #'equal) new-value)
              (puthash position value-cache position-cache)
              new-value))
     ;; Return nil or the non-nil value.