[CI] Use single-GPU runners for ROCm MI3xx CI (#3138)

* Use single-GPU runners for ROCm MI300

* Update ROCM nightly runner to gfx942.1.b

In accordance with label updates in pytorch/pytorch#165115

* Change ROCM nightly runner from gfx942.1.b to gfx942.1.a

* Use correct label

Author: jithunnair-amd

.github/workflows/regression_test_rocm.yml

@@ -21,7 +21,7 @@ jobs:
       matrix:
         include:
           - name: ROCM Nightly
-            runs-on: linux.rocm.gpu.gfx942.2
+            runs-on: linux.rocm.gpu.gfx942.1
             torch-spec: '--pre torch --index-url https://download.pytorch.org/whl/nightly/rocm7.0'
             gpu-arch-type: "rocm"
             gpu-arch-version: "7.0"