feat: add new checks for debian12

systemd_timesyncd_is_enabled_and_running.sh	-> 2.3.2.2
rpcbind_is_disabled.sh				-> 2.1.12
ftp_client_not_installed.sh			-> 2.2.6
chrony_with_chrony_user.sh			-> 2.3.3.2
ipv6_is_enabled.sh				-> 3.1.1

bin/hardening/use_time_sync.sh

@@ -25,7 +25,7 @@ audit() {
     for PACKAGE in $PACKAGES; do
         is_pkg_installed "$PACKAGE"
         if [ "$FNRET" -eq 0 ]; then
-            let count=$((count + 1))
+            count=$(("$count" + 1))
         fi
     done
     if [ "$count" -eq 0 ]; then