[Test] Modify baseline of Qwen3.5-397B-A17B-w4a8-mtp-A2.yaml (vllm-project#11204)

### What this PR does / why we need it?

### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.23.0
- vLLM main:
vllm-project/vllm@dc68bd8

---------

Signed-off-by: Wangbei25 <wangbei41@huawie.com>
Co-authored-by: Wangbei25 <wangbei41@huawie.com>

Author: Wangbei25

tests/e2e/nightly/single_node/models/configs/Qwen3.5-397B-A17B-w4a8-mtp-A2.yaml

@@ -70,5 +70,5 @@ test_cases:
         max_out_len: 1500
         batch_size: 64
         request_rate: 0
-        baseline: 1050
+        baseline: 800
         threshold: 0.97