input: Write a python function to add corresponding elements of two 2D lists.
  assert matrix_addition([[1,2,3], [4,5,6], [7,8,9]], [[3,4,5], [6,7,8], [9,10,11]]) == [[4, 6, 8], [10, 12, 14], [16, 18, 20]]
  assert matrix_addition([[1,1,1], [1,1,1], [1,1,1]], [[2,2,2], [2,2,2], [2,2,2]]) == [[3, 3, 3], [3, 3, 3], [3, 3, 3]]
  assert matrix_addition([[0,0,0], [0,0,0], [0,0,0]], [[0,0,0], [0,0,0], [0,0,0]]) == [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
output: def matrix_addition(matrix1, matrix2):
      result = []
      for row1, row2 in zip(matrix1, matrix2):
          result.append([x + y for x, y in zip(row1, row2)])
      return result