Bump actions/upload-artifact from 4 to 6 (#5466)

Bumps
[actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.

- vLLM version: v0.13.0
- vLLM main:
5326c89803

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.github/workflows/_e2e_nightly_multi_node.yaml

@@ -286,7 +286,7 @@ jobs:
 
         - name: Upload logs
           if: always()
-          uses: actions/upload-artifact@v4
+          uses: actions/upload-artifact@v6
           with:
             name: ${{ inputs.config_file_path }}-pod-logs
             path: /tmp/vllm*_logs.txt