Calling addStretch followed by addItem leads to QList warning

This is similar to some other bugs that have been filed: QTBUG-103775, QTBUG-85909, QTBUG-79223, but none are exactly the same.

There was a change to cause QList to warn when adding items outside of the range (https://codereview.qt-project.org/registerc/qt/qtbase/+/276371), which affects a few different components.

In this case it is QGraphicsLayout. For example in this code:

QGraphicsLinearLayout* layout = new QGraphicsLinearLayout;
QGraphicsWidget* widget = new QGraphicsWidget;
widget->setLayout(layout);
widget->addStretch();
widget->addItem(new QGraphicsWidget);

This will (as of Qt 5.15) print a (debug-mode) warning "QList::insert(): Index out of range", which I understand will become an assert in Qt 6.

Is this code valid? If so, is it possible to make it not warn/assert? I am concerned that this case isn't accounted for with the QList change. (Example now attached)