input: Write a function to take as input two array of integers and swap their elements.
  assert swap([3, 5, 6, 9], [2, 4, 7, 8]) == ([2, 4, 7, 8], [3, 5, 6, 9])
  assert swap([1, 2, 3], [4, 5, 6]) == ([4, 5, 6], [1, 2, 3])
  assert swap([10, 20], [30, 40]) == ([30, 40], [10, 20])
  assert swap([1], [2]) == ([2], [1])
  assert swap([], []) == ([], [])
output: def swap(arr1, arr2):
      arr1, arr2 = arr2, arr1
      return arr1, arr2