Need to rebuild Rackspace gitlab runners - plan to move to Ubuntu 24.04

[Andrew Bartlett]

Just a heads up that due to 
https://bugzilla.samba.org/show_bug.cgi?id=15638 I need to rebuild the
GitLab runners we have in Rackspace, so that it still offers a tag that
our jobs will then expect. 

While doing that, if the image is available by then (it isn't yet), I
would like to make our runners run on Ubuntu 24.04 as the runners
(which are booted once per job) will start faster as they won't have as
many updates to run on first boot.

Please let me know if you think that could be a concern.  On the plus
side it should allow the more recent kernel for some more io_uring
testing. 

Naturally I'll check a full private CI run passes before I rebuild for
production.

Andrew,