LAB: check_roadmap_completion_is_cited.sh self-test row hits live GitHub and flakes (PR #2733 is MERGED) #5910

Self-test row 'PR #2733 is MERGED' calls live GitHub; failed once (rc1, 36 cases 1 fail) in quorum lane A on #5901 @2cb969e7c5, passed for lane B. Not caused by #5901. LAB per C324: must not run on a PR/merge/release path; stub gh or move the live row to the nightly lane. Owner: aprender cop to assign. Found by aprender-wsweep.