Update alert structure to match gitlab-ui

- it now matches the alert DOM structure of alert.vue
  in gitlab-ui

app/views/projects/tracings/show.html.haml

@@ -4,8 +4,10 @@
 - if @project.tracing_external_url.present?
   %h3.page-title= _('Tracing')
   .gl-alert.gl-alert-info.gl-mb-5.flex-alert
+    .gl-alert-container
       = sprite_icon('information-o', css_class: 'gl-icon gl-alert-icon gl-alert-icon-no-title')
-    .alert-message
+      .gl-alert-content
+        .gl-alert-body
           = _("Your password isn't required to view this page. If a password or any other personal details are requested, please contact your administrator to report abuse.")
   - jaeger_link = link_to('Jaeger tracing', 'https://www.jaegertracing.io/', target: "_blank", rel: "noreferrer")
   %p.light= _("GitLab uses %{jaeger_link} to monitor distributed systems.").html_safe % { jaeger_link: jaeger_link }