APT sources: add Bullseye security
refs #18492 (closed)
This does not close the aforementioned issue because once !625 (merged) is merged, we'll want to backport this MR to stable.
Based on !622 (merged).
A build from this branch yields a .build-manifest
that's identical to !622 (merged), as expected currently: none of the packages we pull from Bullseye have a security update that's only found in Bullseye security at the moment (because Bullseye just had a point release).
Edited by intrigeri