Increase UCX upper pin to 1.19

[pentschev]

Increase upper UCX pin to 1.19 to allow us supporting UCX 1.18 that is needed for RAPIDS 25.02.

[jameslamb]

The libucx 1.18 wheels haven't actually been published yet.

https://pypi.org/project/libucx-cu12/

The build job from rapidsai/ucx-wheels#17 is stuck waiting for CI runners: https://github.com/rapidsai/ucx-wheels/actions/runs/12914386875

We should wait to merge this until we see CI pass here and use the 1.18 wheels at runtime.

[jameslamb]

I just cancelled CI here to save CI resources... will restart it once we have libucx 1.18 wheels published.

[jameslamb]

Looks like we got UCX 1.18 in conda C++ tests:

...
  + ucx                     1.18.0  hca5d63b_0                 conda-forge            7MB
...

(build link)

and conda Python tests:

...
  + ucx               1.18.0  h53fb5aa_0                        conda-forge            7MB
...

(build link)

and wheel tests:

Successfully installed ... libucx-cu12-1.18.0 ...

(build link)

And everything passed, except jobs that are failing for unrelated conda errors!

I'll re-run that failed job once the other in-progress jobs pass here, then get this merged.

[jameslamb]

/merge