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/publish.yml

@@ -61,7 +61,7 @@ jobs:
       id-token: write
     if: github.event_name == 'release' && github.event.action == 'published'
     steps:
-    - uses: actions/download-artifact@v4
+    - uses: actions/download-artifact@v6
       with:
         pattern: cibw-*
         path: dist
@@ -80,7 +80,7 @@ jobs:
       id-token: write
     if: github.event_name == 'release' && github.event.action == 'published'
     steps:
-    - uses: actions/download-artifact@v4
+    - uses: actions/download-artifact@v6
       with:
         pattern: cibw-*
         path: dist