[ci] fix: fix machine label for nightly_ascend.yml (verl-project#5887)

### What does this PR do?

fix machine label for nightly_ascend.yml

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Author: yyyy2000

.github/workflows/nightly_ascend.yml

@@ -173,7 +173,7 @@ jobs:
   # Test dapo moonlight-16b megatron vllm
   nightlyCI_dapo-moonlight-16b-megatron-vllm_ascend:
     if: github.repository_owner == 'verl-project'
-    runs-on: linux-aarch64-a2-8
+    runs-on: linux-aarch64-a2b3-8
     timeout-minutes: 180 # Increase this timeout value as needed
     container:
       image: swr.ap-southeast-1.myhuaweicloud.com/base_image/ascend-ci/verl/verl:verl-8.5.0-910b-ubuntu22.04-py3.11-latest
@@ -219,4 +219,4 @@ jobs:
       - name: Running nightlyCI_dapo-moonlight-16b-megatron-vllm_ascend
         run: |
           ray stop --force
-          bash tests/special_npu/nightly_ci_ascend/run_dapo_moonlight-16b_megatron_npu.sh
+          bash tests/special_npu/nightly_ci_ascend/run_dapo_moonlight-16b_megatron_npu.sh