[ci][kuberay] Always cleanup KinD cluster (ray-project#27073)

When cleaning up after the k8s operator tests, we should always delete the k8s cluster even if something went wrong (in fact, it's not clear we even need to clean up the resources within the cluster. 

Signed-off-by: Alex Wu <[email protected]>

.buildkite/pipeline.yml

@@ -426,7 +426,7 @@
  - |
  cleanup() {
  if [ "${BUILDKITE_PULL_REQUEST}" = "false" ]; then ./ci/build/upload_build_info.sh; fi
- python python/ray/tests/kuberay/setup/teardown_kuberay.py
+ python python/ray/tests/kuberay/setup/teardown_kuberay.py || true
  kind delete cluster
  }
  trap cleanup EXIT