[diffusion] fix: tiny fix _templated_ring_attention bug (#15053)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Mick <mickjagger19@icloud.com>

python/sglang/multimodal_gen/test/server/testcase_configs.py

@@ -119,6 +119,8 @@ class DiffusionServerArgs:
     custom_validator: str | None = None  # optional custom validator name
     # resources
     num_gpus: int = 1
+    ulysses_degree: int | None = None
+    ring_degree: int | None = None
     # LoRA
     lora_path: str | None = None  # LoRA adapter path (HF repo or local path)
 
@@ -485,6 +487,9 @@ TWO_GPU_CASES_B = [
             warmup_text=1,
             warmup_edit=0,
             num_gpus=2,
+            # test ring attn
+            ulysses_degree=1,
+            ring_degree=2,
         ),
         T2I_sampling_params,
     ),