attrs-strict is a new dependency of swh-model not packaged in debian.

Debian package for attrs is named python3-attr so I named the package python3-attr-strict.

Associated git repository: https://forge.softwareheritage.org/source/python3-attr-strict/

I still need a sysadmin intervention to setup the phabricator hook triggering package build when a new tag is pushed.

$ ssh -p 2222 -t tate.internal.softwareheritage.org phabricator-setup-hook /srv/phabricator/repos/219/ post-receive-debian-deps