Follow-up from "Resolve "Productivity Analytics: Show error message when there is no data instead of empty charts""

The following discussion from !16897 (merged) should be addressed:

• @filipa started a discussion: (+1 comment)

  should we add an aria-label to this? or aria-hidden maybe?

Add aria-label to the icons in https://gitlab.com/gitlab-org/gitlab/blob/master/ee/app/assets/javascripts/analytics/productivity_analytics/components/app.vue