net/kea: update patch for building with libc++ 19

In https://gitlab.isc.org/isc-projects/kea/-/merge_requests/2410,
Francis Dupont noted there were some errors in the unit tests.

These were due to mistakes on my side, so I now made sure all the unit
tests pass (they silently require GoogleTest!), and updated the upstream
merge request. I hope this goes in soon, but it all seems to take a long
time.

PR: 281124
Approved by: apevnev@me.com (maintainer)
MFH: 2024Q3