Bumped Python to 3.8.12

I have downloaded the source tarball to compute the SHA256 sum.
I did check its GPG signature (same key as 3.8.10, that I previously
also checked)

--HG--
branch : heptapod
5 jobs for !46 with topic/heptapod/py-3.8.12 in 78 minutes and 26 seconds (queued for 6 seconds)
latest merge request