Bump actions/download-artifact from 4 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build-rocm-wheel.yml

@@ -127,14 +127,14 @@ jobs:
 
       - name: Download base Docker image (normal mode)
         if: github.event.inputs.debug_mode != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: rocm-base-image
           path: artifacts/docker-image
 
       - name: Download base Docker image (debug mode - from previous run)
         if: github.event.inputs.debug_mode == 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: rocm-base-image
           path: artifacts/docker-image
@@ -230,28 +230,28 @@ jobs:
 
       - name: Download all artifacts (normal mode)
         if: github.event.inputs.debug_mode != 'true' && github.event.inputs.skip_to_job4 != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
 
       - name: Download all artifacts (debug mode - from previous run + current)
         if: github.event.inputs.debug_mode == 'true' && github.event.inputs.skip_to_job4 != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
           run-id: ${{ github.event.inputs.previous_run_id }}
           github-token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Download vLLM wheel from current run (debug mode)
         if: github.event.inputs.debug_mode == 'true' && github.event.inputs.skip_to_job4 != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: vllm-wheel
           path: artifacts/vllm-wheel
 
       - name: Download all artifacts (skip to job 4 mode - from previous run only)
         if: github.event.inputs.skip_to_job4 == 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
           run-id: ${{ github.event.inputs.previous_run_id }}