tests: fix path separator, use g_build_filename()

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230306122751.2355515-2-marcandre.lureau@redhat.com>
1 file changed