[9.18] [CVE-2023-5679] Check dns64 + server-stale short timeout
Check that named correctly returns a synthesized DNS64 answer when the server stale timer triggers for the A lookup. Use a small value for stale-answer-client-timeout (2ms) and delay the A response by 1 second.
As pointed out elsewhere, it makes no sense to merge this test to v9.19 any more, so it will only be merged into v9.18 & v9.16.
Closes #4334 (closed)