在使用项目委托和来自liswidget的信号时，如何保护tablewidget中发生变化的单元格？

from PyQt5.QtWidgets import QApplication, QMainWindow, QTableWidget, QTableWidgetItem, QStyledItemDelegate, QMessageBox
from PyQt5.QtCore import Qt

class CustomDelegate(QStyledItemDelegate):
    def createEditor(self, parent, option, index):
        # 禁用编辑功能
        return None
    
    def setEditorData(self, editor, index):
        # 设置只读属性
        editor.setReadOnly(True)
    
class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        self.tableWidget = QTableWidget(self)
        self.tableWidget.setColumnCount(2)
        self.tableWidget.setRowCount(2)

        delegate = CustomDelegate()
        self.tableWidget.setItemDelegate(delegate)
        
        self.tableWidget.cellChanged.connect(self.onCellChanged)

        self.setCentralWidget(self.tableWidget)
    
    def onCellChanged(self, row, column):
        # 单元格发生变化时的处理
        QMessageBox.warning(self, "警告", "禁止修改已变更的单元格！")

if __name__ == "__main__":
    app = QApplication([])
    window = MainWindow()
    window.show()
    app.exec_()