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] <support@github.com>

Author: dependabot[bot]

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

@@ -121,14 +121,14 @@ jobs:
 
       - name: Download base Docker image (normal mode)
         if: github.event.inputs.reuse_base_wheels != '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 (reuse_base_wheels mode - from previous run)
         if: github.event.inputs.reuse_base_wheels == 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: rocm-base-image
           path: artifacts/docker-image
@@ -141,14 +141,14 @@ jobs:
 
       - name: Download base wheels (normal mode)
         if: github.event.inputs.reuse_base_wheels != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: rocm-base-wheels
           path: artifacts/base-wheels
 
       - name: Download base wheels (reuse_base_wheels mode - from previous run)
         if: github.event.inputs.reuse_base_wheels == 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: rocm-base-wheels
           path: artifacts/base-wheels
@@ -252,35 +252,35 @@ jobs:
 
       - name: Download all artifacts (normal mode)
         if: github.event.inputs.reuse_base_wheels != 'true' && github.event.inputs.publish_only != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
 
       - name: Download all artifacts (reuse_base_wheels mode - from previous run + current)
         if: github.event.inputs.reuse_base_wheels == 'true' && github.event.inputs.publish_only != '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 (reuse_base_wheels mode)
         if: github.event.inputs.reuse_base_wheels == 'true' && github.event.inputs.publish_only != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: vllm-wheel
           path: artifacts/vllm-wheel
 
       - name: Download dependency wheels from current run (reuse_base_wheels mode)
         if: github.event.inputs.reuse_base_wheels == 'true' && github.event.inputs.publish_only != 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           name: dependency-wheels
           path: artifacts/dependency-wheels
 
       - name: Download all artifacts (publish_only mode - from previous run only)
         if: github.event.inputs.publish_only == 'true'
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
           run-id: ${{ github.event.inputs.previous_run_id }}