fix an ambiguity in the grammar from the implementation of extended unpacking
(one which was strangely "resolved" by pgen)
This also kills the unused testlist1 rule and fixes parse tree validation of
extended unpacking.
diff --git a/Misc/NEWS b/Misc/NEWS
index 4b8ad74..e48d8f2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@
Core and Builtins
-----------------
+- Issue #5460: Fix an ambiguity in the grammar.
+
- Issue #1766304: Improve performance of membership tests on range objects.
- Issue #6713: Improve performance of integer -> string conversions.