qml: disable asynchronous in `DragItem` image as a Qt bug workaround

modules/gui/qt/widgets/qml/DragItem.qml

@@ -466,6 +466,9 @@ Item {
                 borderColor: theme.border
                 fillMode: Image.PreserveAspectCrop
 
+                // FIXME: Qt bug, asynchronous + texture provider + custom shader does not work properly with `grabToImage()`:
+                asynchronous: false
+
                 readonly property real eDPR: MainCtx.effectiveDevicePixelRatio(Window.window)
                 property bool _triggerReadiness: false