wmf:Staff and contractors shows a few people with "QA" in their titles dispersed across the organization. There might be a question where "Quality" is lead in the organization.
Topic on Talk:Wikimedia Release Engineering Team/Archive 2
Valid question.
Most of the people on the staff page with "QA" in their title are doing exploratory QA work (at least partially if not fully). There is even one "QA" section in the Audiences vertical with one staff member doing that work. Those individuals report within their vertical (iow: not to Release Engineering).
Quality, as the larger topic and practice, is currently lead by the Release Engineering Team, specifically by Zeljko and Jean-Rene. There is a monthly "QA Tribe" meeting lead by Jean-Rene to give all of the dispersed QA (and Quality interested people) a place to share wisdom and pain points.