[Regr: 6.8 -> 6.9.0] QQuickWidget background color is pure black with QSGRendererInterface::OpenGL

op//代码占位符
#include "mainwindow.h"#include <QApplication>
#include <QQuickStyle>
#include <QQuickWidget>int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QQuickStyle::setStyle("Material");                QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGL);    
      MainWindow w;
    w.show();
    return a.exec();
}