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/ACKS b/Misc/ACKS
index 0a7c8bd..5e4c03a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -990,6 +990,7 @@
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Eugene Toder
 Matias Torchinsky
 Sandro Tosi
 Richard Townsend