Python image tag 3.9-slim-bullseye Not Found

While trying to build https://gitlab.cern.ch/dmwm/wmcore-docs, there was an error with the "pages" pipeline.

ERROR: Job failed: prepare environment: waiting for pod running: pulling image "registry.cern.ch/docker.io/library/python:3.9-slim-bullseye": image pull failed: rpc error: code = NotFound desc = failed to pull and unpack image "registry.cern.ch/docker.io/library/python:3.9-slim-bullseye": failed to resolve reference "registry.cern.ch/docker.io/library/python:3.9-slim-bullseye": registry.cern.ch/docker.io/library/python:3.9-slim-bullseye: not found. Check https://docs.gitlab.com/runner/shells/index.html#shell-profile-loading for more information

Looking in registry.cern.ch/docker.io/library/python, I did not find the 3.9-slim-bullseye tag. The only slim tag is 3.12-slim.

The image tag used in this gitlab-ci should be updated.