Issue #16602: When a weakref's target was part of a long deallocation chain, the object could remain reachable through its weakref even though its refcount had dropped to zero.

Thanks to Eugene Toder for diagnosing and reporting the issue.
diff --git a/Misc/NEWS b/Misc/NEWS
index 0c01e8b..9934212 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -9,6 +9,10 @@
 Core and Builtins
 -----------------
 
+- Issue #16602: When a weakref's target was part of a long deallocation
+  chain, the object could remain reachable through its weakref even though
+  its refcount had dropped to zero.
+
 - Issue #9011: Fix hacky AST code that modified the CST when compiling
   a negated numeric literal.