Revert "Switch add-to-ordered-list to eql"

This reverts commit b4fd857ead.

I misunderstood the purposed of the function.

doc/lispref/lists.texi

@@ -812,7 +812,7 @@ This function sets the variable @var{symbol} by inserting
 @var{element} into the old value, which must be a list, at the
 position specified by @var{order}.  If @var{element} is already a
 member of the list, its position in the list is adjusted according
-to @var{order}.  Membership is tested using @code{eql}.
+to @var{order}.  Membership is tested using @code{eq}.
 This function returns the resulting list, whether updated or not.
 
 The @var{order} is typically a number (integer or float), and the

etc/NEWS

@@ -1861,8 +1861,6 @@ directory instead of the default directory.
 
 * Incompatible Lisp Changes in Emacs 28.1
 
-** 'add-to-ordered-list' now uses 'eql' instead of 'eq'.
-
 ** 'set-process-buffer' now updates the process mark.
 The mark will be set to point to the end of the new buffer.
 

lisp/subr.el

@@ -1973,7 +1973,7 @@ can do the job."
 
 (defun add-to-ordered-list (list-var element &optional order)
   "Add ELEMENT to the value of LIST-VAR if it isn't there yet.
-The test for presence of ELEMENT is done with `eql'.
+The test for presence of ELEMENT is done with `eq'.
 
 The resulting list is reordered so that the elements are in the
 order given by each element's numeric list order.  Elements
@@ -1993,7 +1993,7 @@ The return value is the new value of LIST-VAR."
   (let ((ordering (get list-var 'list-order)))
     (unless ordering
       (put list-var 'list-order
-           (setq ordering (make-hash-table :weakness 'key))))
+           (setq ordering (make-hash-table :weakness 'key :test 'eq))))
     (when order
       (puthash element (and (numberp order) order) ordering))
     (unless (memq element (symbol-value list-var))