title: QStandardItemModel itemChanged not called
body: <p>Using QStandardItemModel in a QTreeView, itemChanged signals are not triggered (for example on rename). If I recall correctly this was functioning in a much earlier PyQt5 version.</p>
  <pre><code>class Main(QMainWindow):
      def __init__(self):
          super().__init__()
          
          self.resize(200, 100)
          self.dataTree = QTreeView(self)
          self.dataTree.setSelectionMode(QAbstractItemView.SingleSelection)
          self.dataTree.resize(200, 100)
          self.dataModel = QStandardItemModel(self.dataTree)
          self.dataModel.setHorizontalHeaderLabels(['Sources'])
          self.dataModelParent = self.dataModel.invisibleRootItem()
          self.dataTree.setModel(self.dataModel)
          self.dataModel.itemChanged.connect(lambda: self.itemChanged)
  
          master = QStandardItem('test1')
          self.dataModel.appendRow(master)
          
      @pyqtSlot(QStandardItem)
      def itemChanged(self, item):
          print('Item Changed')
  
  if __name__ == '__main__':
      app = QApplication(sys.argv)
      mainWindow = QMainWindow()
      Main = Main()
      Main.show()
      app.exec_()
  </code></pre>