Add placeholder loading animation to expand button

Increases the scope of the selector to target all turbo frames, not only the lazy loading turbo frames, in the collection context sidebar.

app/assets/stylesheets/arclight/modules/hierarchy_and_online_contents.scss

@@ -46,8 +46,8 @@ $hierarchy-view-collapse-icon: url("data:image/svg+xml,<svg xmlns='http://www.w3
     display: none;
   }
 
-  turbo-frame[loading]:not([complete]) {
-    &::after {
+  turbo-frame[busy] {
+    &::before {
       @extend .placeholder !optional;
       animation: placeholder-glow 2s ease-in-out infinite;
       content: 'Loading...';