[issue44025] Match doc: Clarify '_' as a soft keyword

[miss-islington]

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


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nosy: +miss-islington
nosy_count: 4.0 -> 5.0
pull_requests: +24562
pull_request: https://github.com/python/cpython/pull/25888

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44025>
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