[Bug][CI] Pin the LTX FP8 quality gate to its established sigma schedule (#5302)

Signed-off-by: mglyn <1203789601@qq.com>

docs/user_guide/examples/online_serving/text_to_video.md

@@ -296,14 +296,14 @@ done
 
 ```bash
 vllm serve Lightricks/LTX-2 --omni --port 8098 \
-    --enforce-eager --flow-shift 1.0 --boundary-ratio 1.0
+    --enforce-eager --boundary-ratio 1.0
 ```
 
 For multi-GPU memory reduction, you can enable HSDP:
 
 ```bash
 vllm serve Lightricks/LTX-2 --omni --port 8098 \
-    --enforce-eager --flow-shift 1.0 --boundary-ratio 1.0 \
+    --enforce-eager --boundary-ratio 1.0 \
     --use-hsdp --hsdp-shard-size 2
 ```