input: Write a function to convert a given string to a different case using the `swapcase()` method, which changes all uppercase letters to lowercase and vice versa. Return the new string after conversion.
  assert convert_string_case("this Is A TeST")=="THIS iS a tEst"
  assert convert_string_case("HeLLo WoRLd")=="hEllO wOrlD"
  assert convert_string_case("PYTHON")=="python"
  assert convert_string_case("")==""
  assert convert_string_case("12345")=="12345"
output: def convert_string_case(s):
      return s.swapcase()