input: Write a function to sort a list of strings based on their length. Return the sorted list.
  assert sort_strings_by_length(["Hello", "World!", "Good", "Morning"])==["Good", "Hello", "Morning", "World!"]
  assert sort_strings_by_length(["Python", "is", "fun"])==["is", "fun", "Python"]
  assert sort_strings_by_length(["a", "very", "big", "elephant"])==["a", "very", "big", "elephant"]
  assert sort_strings_by_length([])==[]
  assert sort_strings_by_length(["short", "shorter", "shortest"])==["short", "shorter", "shortest"]
output: def sort_strings_by_length(strings):
      return sorted(strings, key=len)