The tag is present in Lintian version 2.109.6. That is the most recent version we know about.
The package appears to use
py3versions -s to determine
the "supported" Python versions without specifying
as a build-dependency.
With only the default version of Python installed, the package may build and test successfully but subsequently fail at runtime when another, non-default, Python version is present.
python3-all as a build-dependency.