Now that ubuntu-24 is out of beta at Github
Since for ubuntu_build, we only use one OS version
and the changes between versions are not as drastic as with MacOS,
it seems safe to have it upgrade automatically.
* CI: Bump OS versions
Github released ubuntu-22.04 and macos-12 from beta
and deprecated ubuntu-18.04 and macos-10.15, due to dropping by 2013.
* CI: clean up installed packages
Now the setup is to add to both rc and profile:
1) set PYENV_ROOT
(can do it unconditionally -- since if you change it,
you need to update all places anyway since any of them can be run first)
2) Add `pyenv` to PATH if not already there
3) eval "$(pyenv init -)"
Not a breaking change, old setup will continue to work.
