[issue41293] fix confusing example in hashlib docs

[Pavel Trukhanov]

Change by Pavel Trukhanov <pavel.trukhanov at gmail.com>:


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type:  -> enhancement
versions: +Python 3.10, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41293>
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