[docs] [issue37209] Add what's new entries for pickle enhancements

[Pierre Glaser]

Change by Pierre Glaser <pierreglaser at msn.com>:


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keywords: +patch
pull_requests: +14319
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/14503

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37209>
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