Fix processing of compacted single-item JSON-LD collections (#28816)

app/services/activitypub/fetch_replies_service.rb

@@ -26,9 +26,9 @@ class ActivityPub::FetchRepliesService < BaseService
 
     case collection['type']
     when 'Collection', 'CollectionPage'
-      collection['items']
+      as_array(collection['items'])
     when 'OrderedCollection', 'OrderedCollectionPage'
-      collection['orderedItems']
+      as_array(collection['orderedItems'])
     end
   end