Add SPDX license (but not copyright) headers to all files which follow a
certain pattern in their existing non-machine-readable header comment.
This commit was entirely generated using the command:
```
git ls-files glib/tests/*.c | xargs perl -0777 -pi -e 's/\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/\n \*\n \* SPDX-License-Identifier: LGPL-2.1-or-later\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/igs'
```
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #1415
glib/tests/scannerapi.c: In function ‘test_scanner_tokens’:
glib/tests/scannerapi.c:124:17: error: comparison of integer expressions of different signedness: ‘guint’ {aka ‘unsigned int’} and ‘gint’ {aka ‘const int’}
124 | for (i = 1; i < tokbuflen; i++)
| ^
