input: Write a python function to filter out negative numbers from a list.
  assert filter_nonnegative([-3, -2, 0, 4, 5])==[0, 4, 5]
  assert filter_nonnegative([-10, -5, 0, 1, 2, 3])==[0, 1, 2, 3]
  assert filter_nonnegative([1, -1, -2, 2, -3, 3])==[1, 2, 3]
output: def filter_nonnegative(numbers):
      return [num for num in numbers if num >= 0]