Make the snowflake deb more accessible to Debian stable users

We made a Snowflake deb in #19409 (closed) and it is apparently now in Debian sid:
https://tracker.debian.org/pkg/snowflake

Yay!

These versions are only in sid, right? Do we have a path in mind for normal Debian users to be able to install this deb? In particular, either a debian backports repository, or our deb.torproject.org repo.

(We have a policy that we only take things from Debian for our deb.tpo repo, but I think we would be following that policy here, since that deb is in Debian, it's just only in sid.)