[ci] [multi-step] narrow multi-step test dependency paths (vllm-project#7760)

Author: SolitaryThinker

.buildkite/test-pipeline.yaml

@@ -312,12 +312,20 @@ steps:
   - CUDA_VISIBLE_DEVICES=0,1 pytest -v -s test_sharded_state_loader.py
   - CUDA_VISIBLE_DEVICES=0,1 pytest -v -s distributed/test_utils.py
 
-- label: Multi-step Tests (4 GPUs) # 10min
+- label: Multi-step Tests (4 GPUs) # 21min
   working_dir: "/vllm-workspace/tests"
   num_gpus: 4
   source_file_dependencies:
-  - vllm/
-  - tests/multi_step/test_correctness.py
+  - vllm/model_executor/layers/sampler.py
+  - vllm/sequence.py
+  - vllm/worker/worker_base.py
+  - vllm/worker/worker.py
+  - vllm/worker/multi_step_worker.py
+  - vllm/worker/model_runner_base.py
+  - vllm/worker/model_runner.py
+  - vllm/worker/multi_step_model_runner.py
+  - vllm/engine
+  - tests/multi_step
   commands:
   - pytest -v -s multi_step/test_correctness.py