Fix missing prototype.
 
--- pilot-link-0.12.4/tests/packers.c	2005-06-16 16:38:28.000000000 +0100
+++ pilot-link-0.12.4/tests/packers.c	2025-07-05 03:28:26.718715118 +0100
@@ -20,6 +20,7 @@
 #include "pi-dlp.h"
 #include "pi-expense.h"
 #include "pi-mail.h"
+#include "pi-debug.h"
 
 unsigned char seed;
 char *target;