[Misc] Fix Current vLLM config is not set. warnings, assert to avoid issues in the future (#31747)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Signed-off-by: Lucas Wilkinson <LucasWilkinson@users.noreply.github.com>
Co-authored-by: Luka Govedič <ProExpertProg@users.noreply.github.com>

tests/v1/kv_offload/test_cpu_gpu.py

@@ -50,6 +50,7 @@ NUM_MAPPINGS = [3]
 @pytest.mark.parametrize("device", CUDA_DEVICES)
 @torch.inference_mode()
 def test_transfer(
+    default_vllm_config,
     gpu_to_cpu: bool,
     num_mappings: int,
     head_size: int,