Merge branch '36452-milestone-icon' into 'master'

Use new MR icon for milestone sidebar

Closes #36452

See merge request !14004

app/views/shared/milestones/_sidebar.html.haml

@@ -88,7 +88,7 @@
     .block.merge-requests
       .sidebar-collapsed-icon
         %strong
-          = icon('exclamation', 'aria-hidden': 'true')
+          = custom_icon('mr_bold')
         %span= milestone.merge_requests.count
       .title.hide-collapsed
         Merge requests