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
This bug only gets triggered on BSD, because it calls `recv_message()`
with `G_IO_HUP | G_IO_IN`. That takes two code paths in
`recv_message()`, and ends up calling `shutdown_source()` twice. The
second call causes a critical warning.
Fixes: https://gitlab.gnome.org/GNOME/glib/-/jobs/2004192
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
