[CI] Add pytest markers to current tests and update the doc. (#577)

Signed-off-by: Alicia <115451386+congw729@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/worker/test_gpu_generation_model_runner.py

@@ -1,7 +1,10 @@
+import pytest
 import torch
 
 from vllm_omni.worker.gpu_generation_model_runner import GPUGenerationModelRunner
 
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
 
 class _DummyInputBatch:
     def __init__(self):