Guix Docker image inflation

[Stephen Scheck <singularsyntax@gmail.com>]

Hello,

As an exercise, I set up daily Guix System Docker image builds using GitLab
and Docker Hub, here:
https://hub.docker.com/repository/registry-1.docker.io/singularsyntax/guix/tags?page=1

The build process works as follows: if an existing `latest` image does not
exist for a given branch (master, 1.1.0, etc.), then bootstrap an image by
running `guix system docker-image` inside an Alpine Linux Docker container
with a fresh Guix installation. Using this image as a seed, `guix pull` is
run for the desired branch, and the resulting image is committed to the
Docker repository. If a "latest" image does exist, it is used instead as
the base from which to run `guix pull`. Daily images are thus built
incrementally from the previous day's build. For anybody curious about the
process, the build script can be browsed here:
https://gitlab.com/singularsyntax-docker-hub/guix/-/blob/master/.gitlab-ci.yml

It works pretty well, except that I'm observing substantial image size
inflation day-over-day, starting at ~197 MB from the seed image, now up to
1.71 GB eleven days later despite running `guix gc --delete-generations`,
`guix gc --collect-garbage`, and `guix gc --optimize` after pulling prior
to committing each new image.

I'm wondering if there is some other Guix GC operation or option I'm
missing, or any other suggestions which could stop this unsustainable image
bloat from occurring. I really do doubt that the Guix System itself is
growing this quickly.