QmlDesigner: Disable QML cache

See: QDS-8861

Task-number: QDS-9110
Change-Id: I654c7e6a961d9791533564593906323149d2395b
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/app/main.cpp

@@ -502,6 +502,8 @@ int main(int argc, char **argv)
         }
     }
 
+    qputenv("QML_DISABLE_DISK_CACHE", "true");
+
     qputenv("QSG_RHI_BACKEND", "opengl");
     QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
                 Qt::HighDpiScaleFactorRoundingPolicy::Round);