fix: nil: Add missing dumpnode call in dnssec-signzone

When the out of zone name was skipped, to prevent it being signed,
dumpnode was not being called to preserve the contents of the node.

This call was missing from "[CVE-2026-11721] sec: usr: Invalid
signed wildcard records were being accepted"

Merge branch '5871-confidential-followup' into 'security-main'

See merge request isc-private/bind9!1081