Merge branch 'ph/477421/suggestionsZIndex' into 'master'

Fixes merge request suggestions dropdown z-index

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/162021



Merged-by: Kushal Pandya <kushal@gitlab.com>
Approved-by: Kushal Pandya <kushal@gitlab.com>
Co-authored-by: Phil Hughes <me@iamphill.com>

app/assets/stylesheets/pages/notes.scss

@@ -344,6 +344,7 @@ $system-note-icon-m-left: $avatar-m-left + $icon-size-diff / $avatar-m-ratio;
 
       .suggestions {
         margin-top: 4px;
+        z-index: auto;
       }
     }