CI: Skip test_ntp_clock_synchronized on Ubuntu 24.04

This test often fails on Ubuntu 24.04 [1], making it difficult to merge
patches. Skip this test until we force time synchronisation.

[1] https://zuul.opendev.org/t/openstack/builds?job_name=kayobe-overcloud-host-configure-ubuntu-noble&project=openstack/kayobe

Change-Id: I222ad8e7ed66cde1f3fb225fa5cdc30c7ed80c99