Needed for subsequent change that will check and error out if the
version is lower than 3.16. We do that to ensure all policies
introduced by CMake up to version 3.16 have their behavior set to
NEW.

Pick-to: 6.2
Task-number: QTBUG-95018
Change-Id: I43575e48cb4ddb70b80f09e0432a2f88b01bec86
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>