input: Write a python function to check for a win in a tic-tac-toe game.
  assert check_win(["X", "X", "X", "_", "_", "_", "_", "_", "_"]) == (True, "X")
  assert check_win(["O", "_", "_", "O", "_", "_", "O", "_", "_"]) == (True, "O")
  assert check_win(["X", "_", "_", "_", "X", "_", "_", "_", "X"]) == (True, "X")
  assert check_win(["_", "_", "_", "_", "_", "_", "_", "_", "_"]) == (False, None)
output: def check_win(board):
      # Winning combinations
      win_combinations = [
          [0, 1, 2], [3, 4, 5], [6, 7, 8],  # Horizontal wins
          [0, 3, 6], [1, 4, 7], [2, 5, 8],  # Vertical wins
          [0, 4, 8], [2, 4, 6]              # Diagonal wins
      ]
      
      # Check for wins
      for combo in win_combinations:
          if board[combo[0]] == board[combo[1]] == board[combo[2]] and board[combo[0]] != "_":
              return (True, board[combo[0]])
      
      return (False, None)