Add support for Python 3.11.6

[edmorley]

Release announcement:
https://blog.python.org/2023/10/python-3116-is-now-available.html
https://www.python.org/downloads/release/python-3116/
https://docs.python.org/release/3.11.6/whatsnew/changelog.html#python-3-11-6

Binary builds:
https://github.com/heroku/heroku-buildpack-python/actions/runs/6383755199

GUS-W-12345424.

[edmorley]

Updated versions on:
https://devcenter.heroku.com/articles/python-support#specifying-a-python-version
https://devcenter.heroku.com/articles/python-runtimes#selecting-a-runtime

Published on changelog:
https://devcenter.heroku.com/changelog-items/2696