fix: test: Wait for the committed NSEC3 chain state in the nsec3 tests

Prior to this fix, the `nsec3` system test could fail due to a test race. The NSEC3 chain is updated asynchronously, and waiting for the keymgr to be done with the zone isn't sufficient to check that the NSEC3 chain has been updated. Wait for the NSEC3PARAM to be published to ensure the zone is in its final signed state.

Example failure: https://gitlab.isc.org/isc-projects/bind9/-/jobs/7819249

Merge branch 'nicki/nsec3-wait-for-committed-chain' into 'main'

See merge request isc-projects/bind9!12487