input: Write a python function to reverse the elements of a stack.
  assert reverse_stack([1, 2, 3]) == [3, 2, 1]
  assert reverse_stack([4, 5, 6, 7]) == [7, 6, 5, 4]
  assert reverse_stack([10, 20, 30]) == [30, 20, 10]
output: def reverse_stack(stack):
      return stack[::-1]