Use more recent SBCL releases in CI pipeline

[sdilts]

We currently use Fedora for the CI pipeline. However, Fedora doesn't routinely update it's SBCL version, which leads to issues like #36 slipping past the CI tests.

The options that I've found so far are:

1. Build SBCL in the pipeline.
2. Use a better distro that generally keeps SBCL more up to date:

• Alpine Linux seems to keeps theirs up more up to date: https://pkgs.alpinelinux.org/packages?name=sbcl&branch=edge&repo=&arch=&maintainer=.
• Guix seems to keep a higher version too: https://packages.guix.gnu.org/packages/sbcl/. Building a Guix container image seems to be tricky, but Nyxt just installs Guix on top of Ubuntu and just uses that: https://github.com/atlas-engineer/nyxt/blob/master/.github/workflows/guix-tests.yml.