Does someone want to propose a fix?

$ ./python -m test -v test_collections 
(...)
test_issue_4920 (test.test_collections.TestCollectionABCs) ... /home/vstinner/python/master/Lib/test/test_collections.py:1518: DeprecationWarning: Please use assertEqual instead.
  self.assertEquals(len(s), len(items) - 1)
ok
(...)
Tests result: SUCCESS


Warning introduced by PR 25209:

commit 453074c8daf996b1815a0cd2218f0dbf1801056c
Author: Stepan Sindelar <me@stevesindelar.cz>
Date:   Thu Apr 8 01:31:55 2021 +0200

    Fix broken test for MutableSet.pop() (GH-25209)
    
    Changes the test to not assert concrete result of pop, but just that it
    was an item from the set, and that the set shrunk by one.