Apply experimental Lintian patch to the infra and enable the new flag.

See https://salsa.debian.org/lintian/lintian/-/merge_requests/311 for
more details. I will update the infra as needed, and once it is in a
released version of Lintian, I will backport it to Focal and install on
the infra.

templates/package-stable.xml

@@ -72,7 +72,7 @@ git clone https://phab.lubuntu.me/source/ci-tooling.git tooling;
       <command>
 export VERSION=&quot;$(head -1 {{ NAME }}/debian/changelog | sed -n &apos;/(/,/)/{:a; $!N; /)/!{$!ba}; s/.*(\([^)]*\)).*/\1/p}&apos; | cut -d &apos;-&apos; -f1)&quot;;
 pull-ppa-debs --ppa=ppa:lubuntu-ci/stable-ci-proposed {{ NAME }} $VERSION-0ubuntu1~ppa1;
-lintian -EvIL +pedantic *.dsc *.deb;
+lintian --fail-on=warning -EvIL +pedantic *.dsc *.deb;
       </command>
       <unstableReturn>1</unstableReturn>
     </hudson.tasks.Shell>

templates/package-unstable.xml

@@ -72,7 +72,7 @@ git clone https://phab.lubuntu.me/source/ci-tooling.git tooling;
       <command>
 export VERSION=&quot;$(head -1 {{ NAME }}/debian/changelog | sed -n &apos;/(/,/)/{:a; $!N; /)/!{$!ba}; s/.*(\([^)]*\)).*/\1/p}&apos; | cut -d &apos;-&apos; -f1)&quot;;
 pull-ppa-debs --ppa=ppa:lubuntu-ci/unstable-ci-proposed {{ NAME }} $VERSION-0ubuntu1~ppa1;
-lintian -EvIL +pedantic *.dsc *.deb;
+lintian --fail-on=warning -EvIL +pedantic *.dsc *.deb;
       </command>
       <unstableReturn>1</unstableReturn>
     </hudson.tasks.Shell>