Merge branch '329888-css-for-pipelines-dark-mode' into 'master'

Remove a weird white border from Pipelines page in dark mode

See merge request gitlab-org/gitlab!60936

app/assets/stylesheets/page_bundles/pipelines.scss

@@ -182,11 +182,6 @@ button.gl-button.btn-link.mini-pipeline-graph-dropdown-toggle {
     border-bottom-color: $border-color;
   }
 
-  &::after {
-    margin-top: 1px;
-    border-bottom-color: $white;
-  }
-
   /**
    * Center dropdown menu in mini graph
    */