Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v5...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>

.github/workflows/build-wheels.yaml

@@ -207,7 +207,7 @@ jobs:
           allow-prereleases: true
 
       - name: Download wheels from artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           pattern: wheels-*
           merge-multiple: true
@@ -260,13 +260,13 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Download sdist artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: sdist
           path: dist
 
       - name: Download wheels artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           pattern: wheels-*
           merge-multiple: true