Custom Build host OS

Currently there doesn’t seem to be a way to use another OS than the ones given by Github. However, I would like to use Arch Linux to build my software since Ubuntu fails horribly to provide a clean build environment. I can understand that it might not be possible to provide every OS the user wants, but maybe it could be possible to run an entire job in a docker container?

You can specify a container to run your job in using the container property