[AIRFLOW-XXX] Fix example "extras" field in mysql connect doc (#5285)
[AIRFLOW-XXX] Fix example "extras" field in mysql connect doc (#5285)


(cherry picked from commit be70175441abbe68e9d5bceb9f13c255684d5147)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow