Use Alpine 3.20 as our base image
Previously we were using Alpine 3.18 which has reached it's end-of-life. The change to 3.20 should have no impact on anyone unless they are using this image as the base image for another image.
Drop Fedora 39 support
Fedora 39 has reached its end of life date. We've dropped it as a supported platform for ponyc and ponyup.
For ponyup that means, we no longer test against it when doing CI. Additinally, new installations of ponyup on Fedora 39 and related platforms won't recognize it as a supported package. If you install ponyup on such a platform, you'll need to set the platform to fedora39 yourself.
For ponyc the lack of support means that if you are using ponyup on Fedora 39 that it won't be able to install any version of ponyc from the point that we stopped supporting Fedora 39 for ponyc. Any ponyc from 0.58.8 on will not be able to be installed via ponyup and will need to instead be built from source.