Function dismiss_by_user_id_and_course_id 

pub async fn dismiss_by_user_id_and_course_id(
    conn: &mut PgConnection,
    user_id: Uuid,
    course_id: Uuid,
) -> ModelResult<SuspectedCheaters>

Dismisses the suspicion against a student (marks it a false alarm), clears the “needs to be reviewed” flag on their completions, and restores any grade that a prior cheating confirmation had failed (a no-op if the student was never confirmed). Atomic.