No longer mark -cycle as pureexternals/dash

See https://bugs.gnu.org/80456.  This is similar but not identical
to #405 and https://bugs.gnu.org/64127 in that it involves a
problematic compile-time constant produced from a pure function:

  (--map (-take 5 it) (-split-at 5 (-cycle '(1 2 3))))
  =>
  dev/examples.el: Error: List contains a loop: (3 1 2 3 1 . #2)

* dash.el (-cycle): No longer mark as pure.
* NEWS.md: Announce change.

1 files changed, 1 insertions, 1 deletions

diff --git a/dash.el b/dash.el
index ea7fece..41d1e53 100644
--- a/dash.el
+++ b/dash.el
@@ -1893,7 +1893,7 @@ LISTS, it is generally recommended to use `-unzip-lists' instead."
   "Return an infinite circular copy of LIST.
 The returned list cycles through the elements of LIST and repeats
 from the beginning."
-  (declare (pure t) (side-effect-free t))
+  (declare (side-effect-free t))
   ;; Also works with sequences that aren't lists.
   (let ((newlist (append list ())))
     (nconc newlist newlist)))