input: Write a function to filter negative numbers from a list.
  assert filter_negative([1, -2, 3, -4, 5, -6]) == [1, 3, 5]
  assert filter_negative([-10, -20, -30, -40]) == []
  assert filter_negative([0, 2, -3, 5, -1]) == [0, 2, 5]
output: def filter_negative(numbers):
      return [num for num in numbers if num >= 0]