[docs] [issue35631] Improve typing docs wrt abstract/concrete collection types

[Ville Skyttä]

Change by Ville Skyttä <ville.skytta at iki.fi>:


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keywords: +patch, patch, patch
pull_requests: +10774, 10775, 10776
stage:  -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35631>
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