input: Write a python function to sort a list of strings by their length.
  assert sort_strings_by_length(['foo', 'bar', 'baz', 'foobar', 'beer', 'wine'])==['foo', 'bar', 'baz', 'beer', 'wine', 'foobar']
  assert sort_strings_by_length(['a', 'abcde', 'abcd', 'ab', 'abcdef'])==['a', 'ab', 'abcd', 'abcde', 'abcdef']
  assert sort_strings_by_length(['apple', 'banana', 'cherry', 'date'])==['date', 'apple', 'cherry', 'banana']
output: def sort_strings_by_length(strings):
      return sorted(strings, key=len)