dns/void-zones-tools: fix unbound-killing bug

void-zones-tools downloads a set of pre-defined lists of undesirable
domains and creates "voided" dns zones for Unbound, blocking access to
these domains via dns.

One of the default lists is no longer maintained, and was removed from
the upstream code. However, there hasn't been released a new version
after the change was made, thus the port has not been updated.
This has not been a problem up until now because the update script has
been downloading an empty file, essentially a no-op in the zone
creation/loading, but at some point today it started serving a domain
parking page, and the HTML of that page is being dumped into the dns
zone file resulting in parse errors and Unbound cannot start.

While waiting for upstream to tag a new version, I changed the port to
track the latest GitHub commit. This fixes the issue for now.

PR: 274027
Upstream issue: https://github.com/cyclaero/void-zones-tools/issues/12
Reported by: Robert William Vesterman <bob@vesterman.com>
MFH: 2023Q3

(cherry picked from commit 27c31c5386f115976bd436e42566539e42be2b21)