Draft: Salsa-CI: Re-enable backports for Bookworm and Bullseye

This MR is left as a draft/reminder about the option to revert "Salsa-CI: Remove backports builds that became incompatible in 58a75348" (commit 41875d56) in the future on a backports branch (for Bookworm, Bullseye or Ubuntu 22.04 Focal) in case backports are needed.