check_ci_wait_cancel.sh inherits EVT from the x86-main step env (run 39888226186)

scripts/check_ci_wait_cancel.sh:72 uses EVT="${EVT:-merge_group}"; the x86-main step env sets EVT=pull_request, so the 4 merge_group rows (determinism/guards cancelled, guards red, guards skipped) run as PR rows and exit 0. Repro: EVT=pull_request bash scripts/check_ci_wait_cancel.sh. Fix: row event from its own variable + a must-fail leak row. Epic #5923.