[issue23493] optimize sort_keys in json module by using operator.itemgetter()

[INADA Naoki]

Change by INADA Naoki <songofacandy at gmail.com>:


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keywords: +patch
pull_requests: +7709
stage:  -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue23493>
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