input: Write a python function to normalize a list of strings to lowercase.
  assert normalize(['Hello', 'WORLD', 'Python']) == ['hello', 'world', 'python']
  assert normalize(['APPLE', 'Banana', 'CHERRY']) == ['apple', 'banana', 'cherry']
  assert normalize(['TeSt', 'CaSe', 'sEnSiTiVe']) == ['test', 'case', 'sensitive']
output: def normalize(lst):
      return [s.lower() for s in lst]