refactor: streamline item filtering in DataListStudentShort initialization

lab2/data_list_student_short.rb

@@ -3,8 +3,8 @@ require_relative './data_table'
 class DataListStudentShort < DataList
   def initialize(items)
     column_names = ['№', 'Фамилия и инициалы', 'Телефон', 'Telegram', 'Email']
-    super(items.select { |item| item.is_a?(StudentShort) }, column_names)
-    @items = filtered.dup
+    filtered = items.select { |item| item.is_a?(StudentShort) }
+    super(filtered, column_names)
   end
 
   def items=(new_items)