input: Write a function to swap the values of two variables. The function should take two variables as input and return them with their values swapped.
  assert swap_variables(5, 10) == (10, 5)
  assert swap_variables(0, 0) == (0, 0)
  assert swap_variables(-3, 7) == (7, -3)
  assert swap_variables(100, -100) == (-100, 100)
  assert swap_variables("hello", "world") == ("world", "hello")
output: def swap_variables(a, b):
      return b, a