tst_QAccessibilityLinux: port away from Q_FOREACH

The single Q_FOREACH use here is simple, as it's over a local variable
that just isn't marked as const due to the way it's constructed, and
the loop body clearly doesn't modify the container, so the protective
copy that Q_FOREACH performs is not needed. But std::as_const() is, to
prevent a detach() (attempt). Add that.

Pick-to: 6.6 6.5
Task-number: QTBUG-115839
Change-Id: If228f649efd87388f6e312078b24a5b46ac8dc36
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: David Faure <david.faure@kdab.com>

tests/auto/other/qaccessibilitylinux/tst_qaccessibilitylinux.cpp

@@ -103,7 +103,7 @@ QStringList tst_QAccessibilityLinux::getChildren(QDBusInterface *interface)
 
     Q_ASSERT(interface->property("ChildCount").toInt() == list.count());
     QStringList children;
-    Q_FOREACH (const QSpiObjectReference &ref, list)
+    for (const QSpiObjectReference &ref : std::as_const(list))
         children << ref.path.path();
 
     return children;