bpo-36597: fix random doctest failure (GH-12776)

diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 40bb06a..b9e887c 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -492,7 +492,7 @@
     >>> obj = Object()
     >>> weakref.finalize(obj, print, "obj dead or exiting")  #doctest:+ELLIPSIS
     <finalize object at ...; for 'Object' at ...>
-    >>> exit()                                               #doctest:+SKIP
+    >>> del obj
     obj dead or exiting