Fix REUSE licensing/copyright issues in `tests/utils`

This patch makes `reuse lint` happy for the files in `tests/utils`.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I472089852d8840653c0a4a2350a4d4981329f43e
Reviewed-on: https://review.lttng.org/c/babeltrace/+/11385
Tested-by: jenkins <jenkins@lttng.org>
CI-Build: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Michael Jeanson <mjeanson@efficios.com>