Fix broken test assertion

Author: code-shoily

test/2020/day_23_test.exs

@@ -12,6 +12,6 @@ defmodule AdventOfCode.Y2020.Day23Test do
 
  @tag :skip
  test "Year 2020, Day 23, Part 2" do
- assert Solution.run_2() == nil
+ assert Solution.run_2() == {:not_implemented, 2}
  end
 end