Align ucx version pinning with ucx-py/ucxx. (#704)

As of rapidsai/ucx-py#1032 and rapidsai/ucxx#205, the `ucx` version pinning in RAPIDS has been updated. This PR aligns with those changes.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Jake Awe (https://github.com/AyodeAwe)

URL: #704

conda/recipes/versions.yaml

@@ -15,4 +15,4 @@ numpy_version:
 nvtx_version:
   - '>=0.2.1,<0.3'
 ucx_version:
-  - '>=1.14.1'
+  - '>=1.15.0,<1.16.0'