mediawiki-core-doxygen-publish invokes maintenance/mwdocgen.php which thus depends on mediawiki/vendor to be cloned. That caused the job to fails eventually (bug 72826).
Bryan Davis added the vendor repository to Jenkins Git plugin with https://gerrit.wikimedia.org/r/#/c/170386/
The next step would be to drop the scm: section and use the builder zuul-cloner.
Version: wmf-deployment
Severity: enhancement