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 9e662f6..4500d1a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1067,6 +1067,7 @@
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Eugene Toder
 Erik Tollerud
 Matias Torchinsky
 Sandro Tosi