mysql: add a missing name to a task

mysql/tasks/main.yml

@@ -1,6 +1,7 @@
 ---
 
-- set_fact:
+- name: Set if MySQL should be restart (if needed) or not at all
+  set_fact:
     mysql_restart_handler_name: "{{ mysql_restart_if_needed | bool | ternary('restart mysql', 'restart mysql (noop)') }}"
 
 - include: packages_stretch.yml