Isn't borderline useless compared to mypy and pylint

Nobody should be using Poppler < 0.46

A zip file with a file pointing to /etc/passwd would, upon being cleaned by
mat2, produce a file with the filesystem's /etc/passwd file.

Thanks to Maxime Morin ( https://www.maijin.fr/ )
for the patch.

This should prevent the testsuite from breaking,
and marginally increase fingerprinting resistance.

Kudos to Miguel Angel Marco Buzunariz for the original patch.

This should fix #162

Those issues were found via https://github.com/google/atheris

Contributors are now supposed to run tests in the GitLab instance, so
this also needs to be reflected in the CONTRIBUTING.md as otherwise
people not used to forge workflows could completely miss that
information.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>