Change license in test file

According to QUIP-18 [1], all test files should be
LicenseRef-Qt-Commercial OR GPL-3.0-only

[1]: https://contribute.qt-project.org/quips/18

Pick-to: 6.7
Task-number: QTBUG-121787
Change-Id: I701e707447ca68977bdd80662200eb0c36545dbe
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

tests/auto/cmake/test_standalone_test/tst_standalone_test.cpp

@@ -1,5 +1,5 @@
 // Copyright (C) 2024 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
 
 #include <QTest>
 #include <QWindow>