input: Write a python function to convert the linked list into a Python list.
  assert linked_list_to_list(l) == []
  l.addNode(1)
  assert linked_list_to_list(l) == [1]
  l.addNode(2)
  l.addNode(3)
  assert linked_list_to_list(l) == [1, 2, 3]
output: def linked_list_to_list(linked_list):
      result = []
      current = linked_list.head
      while current:
          result.append(current.data)
          current = current.next
      return result