definitions: Fail on lintian error
Otherwise nobody will ever look at the results.
I'm pretty sure this was the default at some point but clearly isn't anymore:
Fixing these early makes review for PureOS maintainers simpler on e.g. new packaegs. This will certainly create some fallout but if urgency is needed one can always override
L5_LINTIAN_OPTS in the gitlab-ci yml file for the moment.