fix(agentx): bump dsv4 MI355X vllm agentic image to nightly build

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: seungrokj

.github/configs/amd-master.yaml

@@ -641,7 +641,7 @@ kimik2.5-fp4-mi355x-atom:
       - { tp: 4, conc-start: 4, conc-end: 128 }
 
 dsv4-fp4-mi355x-vllm-agentic:
-  image: vllm/vllm-openai-rocm:v0.21.0
+  image: vllm/vllm-openai-rocm:nightly-4f940896a32c9e2a0eba7f50d521bf5f6b4de458
   model: deepseek-ai/DeepSeek-V4-Pro
   model-prefix: dsv4
   runner: mi355x