input: Write a python function to shuffle a list of files and return the first N files.
  assert len(shuffle_files(['file1.mp3', 'file2.mp3', 'file3.mp3'], 2)) == 2
  assert 'file1.mp3' in shuffle_files(['file1.mp3', 'file2.mp3', 'file3.mp3'], 3)
  assert 'file2.mp3' in shuffle_files(['file1.mp3', 'file2.mp3', 'file3.mp3'], 3)
output: import random
  
  def shuffle_files(files, n):
      random.shuffle(files)
      return files[:n]