[regression 5.15 -> 6.0] QApplication::quit() no longer works within closeEvent()

Calling QApplication::quit() from within a widget's closeEvent() no longer has any effect in Qt 6.0.0.

The test case below, with Qt 5, quits when the window is closed. In Qt 6, QApplication::exec() does not return and the application remains running with no windows visible.

Note: It's necessary to do setQuitOnLastWindowClosed(false) to see the issue (otherwise the application quits regardless of QApplication::quit() being called or not).

Test case:

#include <QApplication>
#include <QCloseEvent>
#include <QWidget>

class MyWindow : public QWidget
{
public:
    void closeEvent(QCloseEvent * event) override
    {
        qApp->quit();
        event->accept();
    }
};

int main(int argc, char ** argv)
{
    QApplication app(argc, argv);
    app.setQuitOnLastWindowClosed(false);

    MyWindow window;
    window.show();

    return app.exec();
}