input: Write a python function to return the squares of non-negative numbers from a list using list comprehension.
  assert squares_of_non_negatives([-5, 0, 4, 78, -3]) == [0, 16, 6084]
  assert squares_of_non_negatives([1, -1, 2, -2, 3, -3]) == [1, 4, 9]
  assert squares_of_non_negatives([0, -10, 5, -6, 8]) == [0, 25, 64]
output: def squares_of_non_negatives(lst):
      return [x**2 for x in lst if x >= 0]