letsencrypt: depend on bind9-dnsutils (dnsutils is a trixie transitional)

On Debian 13 trixie `dnsutils` is a transitional package replaced by
`bind9-dnsutils`. Apt installs bind9-dnsutils when you ask for dnsutils,
but `dpkg -s dnsutils` returns 1 because no real package by that name
exists — bw's pkg_apt status check then flags the item as failed every
apply. Switching the dependency to the real package name resolves the
loop.

The bundle just needs `nsupdate` (provided by bind9-dnsutils) for the
DNS-01 challenge hook.

bundles/letsencrypt/metadata.py

@@ -2,7 +2,7 @@ defaults = {
     'apt': {
         'packages': {
             'dehydrated': {},
-            'dnsutils': {},
+            'bind9-dnsutils': {},
         },
     },
     'letsencrypt': {