[issue22823] Use set literals instead of creating a set from a list

[Roundup Robot]

Roundup Robot added the comment:

New changeset 7c2811521261 by Victor Stinner in branch 'default':
Issue #22823: Fix typo in unittest/mock.py
https://hg.python.org/cpython/rev/7c2811521261

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22823>
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