[issue30934] Document how to run coverage for repository idlelib files.

[Tal Einat]

Change by Tal Einat <taleinat+python at gmail.com>:


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keywords: +patch
pull_requests: +21665
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/22694

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue30934>
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