input: Write a python function to check if the board is full.
  assert is_board_full([' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ']) == False
  assert is_board_full([' ', 'X', 'X', 'X', 'O', 'O', 'O', 'X', 'X', 'O']) == True
  assert is_board_full([' ', 'X', 'X', 'X', 'O', 'O', 'O', 'X', 'X', ' ']) == False
output: def is_board_full(board):
      return ' ' not in board