Use CollectionViewTextItem instead of a cast

ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm

Index: ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm
diff --git a/ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm b/ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm
index 91d89ff5b93f50ab35219a547dde88c3acc7d28e..1f414a69ba0cd9fe9decb2a81dc967a516642eed 100644
--- a/ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm
+++ b/ios/chrome/browser/ui/reading_list/reading_list_collection_view_controller.mm
@@ -276,20 +276,6 @@ using ItemsMapByDate = std::multimap<int64_t, ReadingListCollectionViewItem*>;
 
 #pragma mark - UICollectionViewDelegate
 
-- (UICollectionReusableView*)collectionView:(UICollectionView*)collectionView
-          viewForSupplementaryElementOfKind:(NSString*)kind
-                                atIndexPath:(NSIndexPath*)indexPath {
-  UICollectionReusableView* cell = [super collectionView:collectionView
-                       viewForSupplementaryElementOfKind:kind
-                                             atIndexPath:indexPath];
-  MDCCollectionViewTextCell* textCell =
-      base::mac::ObjCCast<MDCCollectionViewTextCell>(cell);
-  if (textCell) {
-    textCell.textLabel.textColor = [[MDCPalette greyPalette] tint500];
-  }
-  return cell;
-};
-
 - (void)collectionView:(UICollectionView*)collectionView
     didSelectItemAtIndexPath:(NSIndexPath*)indexPath {
   [super collectionView:collectionView didSelectItemAtIndexPath:indexPath];
@@ -1143,6 +1129,7 @@ using ItemsMapByDate = std::multimap<int64_t, ReadingListCollectionViewItem*>;
       header.text = l10n_util::GetNSString(IDS_IOS_READING_LIST_UNREAD_HEADER);
       break;
   }
+  header.textColor = [[MDCPalette greyPalette] tint500];
   return header;
 }