Doc: Fix position of since marker for QAxSelect::SandboxingAppContainer

The [since] marker is only recognized as the first argument of \value.
Written after the enum value name it silently becomes part of the
description text, without any warning from qdoc:

   https://doc.qt.io/qt-6/10-qdoc-commands-tablesandlists.html#value

Pick-to: 6.12 6.11 6.5
Change-Id: If09d750ee918bc572f9b047fac0c1e705c211fd5
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>