fix: use sglang v0.5.12 release tag instead of dated nightly

Drops the -20260517 nightly suffix so the recipe uses the
lmsysorg/sglang-rocm:v0.5.12-rocm720-mi35x release tag rather than
a date-pinned nightly build.

Author: claude-fix-bot

.github/configs/amd-master.yaml

@@ -124,7 +124,7 @@ dsr1-fp8-mi355x-sglang:
       - { tp: 8, conc-start: 4, conc-end: 64 }
 
 qwen3.5-bf16-mi355x-sglang:
-  image: lmsysorg/sglang-rocm:v0.5.12-rocm720-mi35x-20260517
+  image: lmsysorg/sglang-rocm:v0.5.12-rocm720-mi35x
   model: Qwen/Qwen3.5-397B-A17B
   model-prefix: qwen3.5
   runner: mi355x
@@ -143,7 +143,7 @@ qwen3.5-bf16-mi355x-sglang:
       - { tp: 8, ep: 1, conc-start: 4, conc-end: 256 }
 
 qwen3.5-bf16-mi355x-sglang-mtp:
-  image: lmsysorg/sglang-rocm:v0.5.12-rocm720-mi35x-20260517
+  image: lmsysorg/sglang-rocm:v0.5.12-rocm720-mi35x
   model: Qwen/Qwen3.5-397B-A17B
   model-prefix: qwen3.5
   runner: mi355x