[issue44310] Document that lru_cache uses hard references

[miss-islington]

Change by miss-islington <mariatta.wijaya+miss-islington at gmail.com>:


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pull_requests: +25364
pull_request: https://github.com/python/cpython/pull/26778

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44310>
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