Add @mkozono to backend CODEOWNERS

.gitlab/CODEOWNERS.disabled

 # Backend Maintainers are the default for all ruby files
-*.rb @ayufan @dbalexandre @DouweM @dzaporozhets @godfat @grzesiek @nick.thomas @rspeicher @rymai @smcgivern
-*.rake @ayufan @dbalexandre @DouweM @dzaporozhets @godfat @grzesiek @nick.thomas @rspeicher @rymai @smcgivern
+*.rb @ayufan @dbalexandre @DouweM @dzaporozhets @godfat @grzesiek @mkozono @nick.thomas @rspeicher @rymai @smcgivern
+*.rake @ayufan @dbalexandre @DouweM @dzaporozhets @godfat @grzesiek @mkozono @nick.thomas @rspeicher @rymai @smcgivern
 # Technical writing team are the default reviewers for everything in `doc/`
 /doc/ @axil @marcia