[issue42836] docs: struct: clarify struct caching behaviour

[Roundup Robot]

Change by Roundup Robot <devnull at psf.upfronthosting.co.za>:


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keywords: +patch
nosy: +python-dev
nosy_count: 2.0 -> 3.0
pull_requests: +22992
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/24164

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42836>
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