archive.s.o: change Debian tooltip to include derivatives

The tooltip over the Debian logo at archive.s.o reads "source packages from the Debian distribution", which is no longer correct after the completion of swh/infra/sysadm-environment#2400 (closed). We should make the tooltip more general, here's a concrete proposal: "source packages from Debian and Debian-based distributions".

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Migrated from T3811 (view on Phabricator)