[ci/build] fix broken tests in LLM.collective_rpc (#15350)

Signed-off-by: youkaichao <youkaichao@gmail.com>

.buildkite/test-pipeline.yaml

@@ -515,7 +515,7 @@ steps:
   - vllm/worker/model_runner.py
   - entrypoints/llm/test_collective_rpc.py
   commands:
-  - pytest -v -s entrypoints/llm/test_collective_rpc.py
+  - VLLM_ENABLE_V1_MULTIPROCESSING=0 pytest -v -s entrypoints/llm/test_collective_rpc.py
   - pytest -v -s ./compile/test_basic_correctness.py
   - pytest -v -s ./compile/test_wrapper.py
   - VLLM_TEST_SAME_HOST=1 torchrun --nproc-per-node=4 distributed/test_same_node.py | grep 'Same node test passed'

tests/entrypoints/llm/test_collective_rpc.py

@@ -21,18 +21,9 @@ def test_collective_rpc(tp_size, backend):
     def echo_rank(self):
         return self.rank
 
-    from vllm.worker.worker import Worker
-
-    class MyWorker(Worker):
-
-        def echo_rank(self):
-            return self.rank
-
     llm = LLM(model="meta-llama/Llama-3.2-1B-Instruct",
               enforce_eager=True,
               load_format="dummy",
               tensor_parallel_size=tp_size,
-              distributed_executor_backend=backend,
-              worker_cls=MyWorker)
-    for method in ["echo_rank", echo_rank]:
-        assert llm.collective_rpc(method) == list(range(tp_size))
+              distributed_executor_backend=backend)
+    assert llm.collective_rpc(echo_rank) == list(range(tp_size))