Fix duplicate `debian-bullseye` in image name

What does this MR do and why?

Fixes regression introduced by !586 (merged).

The generate image name is:

registry.gitlab.com/gitlab-org/gitlab-build-images/debian-bullseye-debian-bullseye-ruby-2.7.patched-golang-1.18-node-16.14-postgresql-11:rubygems-3.2-git-2.36-lfs-2.9-chrome-105-yarn-1.22-graphicsmagick-1.3.36

The duplicate debian-bullseye-debian-bullseye happens due to usage of OS and DEBIAN in a CI. Ignore DEBIAN/UBI if OS is specified.

We will have to cleanup those:

• https://gitlab.com/gitlab-org/gitlab-build-images/container_registry/?orderBy=UPDATED&sort=desc&search[]=debian-bullseye-debian-bullseye-&search[]=
• https://gitlab.com/gitlab-org/gitlab-build-images/container_registry/?orderBy=UPDATED&sort=desc&search[]=debian-bullseye-ubi&search[]=