Buster armel only available on archive.debian.org
The Buster repository (https://deb.debian.org/debian/dists/buster/main/) only provides amd64, arm64, armhf and i386. Thus the mainline Salsa-CI has been failing job 'images-prod-arm: [base, arm32v5, buster]' since 915f562e was merged:
Err:4 http://deb.debian.org/debian buster/main armel Packages
404 Not Found [IP: 151.101.162.132 80]
Err:5 http://deb.debian.org/debian buster-updates/main armel Packages
404 Not Found [IP: 151.101.162.132 80]
Switch Buster to use the archive.debian.org mirror which seems to have armhf. Buster is already oldoldstable so switching it to use the archive mirror already now is appropriate. We would need to eventually switch to archive in less than a year anyway.
We should have spotted this already while working on !490 (merged) but somehow we skipped running the pipeline fully or checking it.