Issue #21321: itertools.islice() now releases the reference to the source iterator when the slice is exhausted.

Patch by Anton Afanasyev.
diff --git a/Misc/NEWS b/Misc/NEWS
index f086cc3..ab71e01 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -46,6 +46,9 @@
 Library
 -------
 
+- Issue #21321: itertools.islice() now releases the reference to the source
+  iterator when the slice is exhausted.  Patch by Anton Afanasyev.
+
 - Issue #9291: Do not attempt to re-encode mimetype data read from registry in
   ANSI mode. Initial patches by Dmitry Jemerov & Vladimir Iofik.