input: Write a function to find the smallest even number in a list.
  assert find_smallest_even([1, 2, 3, 4, 5, 6]) == 2
  assert find_smallest_even([10, 15, 22, 13, 8]) == 8
  assert find_smallest_even([7, 11, 3, 5]) == None
  assert find_smallest_even([4, 6, 2, 8, 12]) == 2
output: def find_smallest_even(numbers):
      even_numbers = [num for num in numbers if num % 2 == 0]
      return min(even_numbers, default=None)