Demise of Ursabot CI jobs

[Wes McKinney <we...@gmail.com>]

hi folks -- I just wanted to confirm that the Ursabot CI jobs that
went down a few weeks ago won't be coming back, at least not in the
Buildbot form factor. The Buildbot master was hosted on a physical
machine which suffered some kind of network configuration problem
during a Linux update that I don't have the sysadmin skills to
resolve, so that machine has been wiped and with it the Buildbot
setup.

There are some jobs that were being run on these machines (CUDA, large
memory tests) that still need to be run. I highly recommend that we
move these to physical machines that report in to our free Buildkite
org (https://buildkite.com/apache-arrow), that way things will be less
brittle and machines can easily come and go without any involvement
from ASF Infra (which is why I've been against self-hosted GitHub
Actions).

Thanks,
Wes