Update Buildkite pipeline for the new JuliaGPU cluster.

Switch to the per-backend queues of the new JuliaGPU cluster.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: maleadt

.buildkite/pipeline.yml

@@ -6,8 +6,7 @@ steps:
       - JuliaCI/julia-test#v1:
            coverage: false # 1000x slowdown
     agents:
-      queue: "juliagpu"
-      cuda: "*"
+      queue: "cuda"
     timeout_in_minutes: 60
     # Don't run Buildkite if the commit message includes the text [skip tests]
     if: build.message !~ /\[skip tests\]/