CI: Change the runner in SGlang tests (ROCm#1589)

Author: gyohuangxin

.github/workflows/sglang_downstream.yaml

@@ -27,7 +27,7 @@ jobs:
   sglang:
     name: sglang integration
     needs: [check-signal]
-    runs-on: aiter-mi300-1gpu
+    runs-on: aiter-1gpu-runner
     env:
       SGL_BRANCH: v0.5.5
       GPU_ARCH: gfx942