Try this

Gitlab CI allows to specify custom docker image (https://docs.gitlab.com/ee/ci/yaml/index.html#image). Try something that already has systemd inside, like https://github.com/minimum2scp/dockerfiles/tree/master/systemd-bookworm (https://hub.docker.com/r/minimum2scp/systemd-bookworm/).

(But keep in mind, that I just came up with this idea, I never tried using custom docker images in gitlab ci, and never used anything by minimum2scp)