[manylinux2014] Update CPython 3.8 from 3.8.2 to 3.8.3

[manselmi]

Changelog: https://github.com/python/cpython/blob/v3.8.3/Misc/NEWS.d/3.8.3.rst

[manselmi]

The s390x build failed with localedef: command not found but the corresponding line of code last changed 6 months ago, so it looks like this failure must be due to a change in the upstream image s390x/clefos:7. Indeed, it looks like the upstream image was last updated about 7 days ago.

Should this PR still be merged, with someone addressing s390x separately?

[mayeut]

@manselmi,
if you can rebase once #599 gets merged, it would be best to get all CI checks green for this PR.
Thanks

[manselmi]

@mayeut Sounds good, thanks.

[mayeut]

Thanks for the 3 PRs.
I'll merge this one after the setuptools update.