[issue30004] in regex-howto, improve example on grouping

[Mandeep Bhutani]

Change by Mandeep Bhutani <mandeep at keemail.me>:


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keywords: +patch
pull_requests: +4384
stage: needs patch -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue30004>
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