the current version of the package is not in its VCS.
Either you need to push your commits and/or your tags, or the information about
the package's VCS are out of date. A common cause of the latter issue when
using the Git VCS is not specifying the correct branch when the packaging is
not in the default one (remote HEAD branch), which is usually "master" but can
be modified in salsa.debian.org in the project's general settings with the
"Default Branch" field). Alternatively the Vcs-Git field in debian/control can
contain a "-b <branch-name>" suffix to indicate what branch is used
for the Debian packaging.
The Vcs URL git://anonscm.debian.org/debian-science/packages/libsnl.git is deprecated/defunct, https://anonscm.debian.org/git/debian-science/packages/libsnl.git was tried instead. Please update the Vcs field in debian/control.