Relicensed testutils to match other test code

Permission granted in https://github.com/libsdl-org/SDL/commit/76a7b629bfc4869df7659c2f2e47d9253c73696f#commitcomment-121408342

(cherry picked from commit 6c2472d459602eb3c3ee109d6e8f255336109673)
(cherry picked from commit a4ad293d4a184057c6dc370538ddd808ca9b0c90)

test/testutils.c

@@ -1,7 +1,14 @@
 /*
-Copyright 1997-2023 Sam Lantinga
-Copyright 2022 Collabora Ltd.
-SPDX-License-Identifier: Zlib
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+  Copyright 2022 Collabora Ltd.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely.
 */
 
 #include "testutils.h"

test/testutils.h

@@ -1,7 +1,14 @@
 /*
-Copyright 1997-2023 Sam Lantinga
-Copyright 2022 Collabora Ltd.
-SPDX-License-Identifier: Zlib
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+  Copyright 2022 Collabora Ltd.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely.
 */
 
 #ifndef TESTUTILS_H