Update CPython 3.8.{9→10} & 3.9.{4→5} (#1079)
Update CPython 3.8.{9→10} & 3.9.{4→5} (#1079)

Changelogs:

* https://docs.python.org/release/3.8.10/whatsnew/changelog.html
* https://docs.python.org/release/3.9.5/whatsnew/changelog.html
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