Only set graphics API when using Qt6

src/main.cpp

@@ -147,8 +147,10 @@ int main(int argc, char *argv[])
 #ifdef HAVE_WEBVIEW
     QtWebView::initialize();
     QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+#if QT_VERSION > QT_VERSION_CHECK(6, 0, 0)
     QQuickWindow::setGraphicsApi(QSGRendererInterface::OpenGLRhi);
 #endif
+#endif
 
 #ifdef Q_OS_ANDROID
     QGuiApplication app(argc, argv);