meta: bump actions/download-artifact from 5.0.0 to 6.0.0

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@634f93c...018cc2c)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-tarball.yml

@@ -91,7 +91,7 @@ jobs:
       - name: Environment Information
         run: npx envinfo
       - name: Download tarball
-        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0  # v5.0.0
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53  # v6.0.0
         with:
           name: tarballs
           path: tarballs

.github/workflows/test-shared.yml

@@ -113,7 +113,7 @@ jobs:
     name: '${{ matrix.system }}: with shared libraries'
     runs-on: ${{ matrix.runner }}
     steps:
-      - uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0  # v5.0.0
+      - uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53  # v6.0.0
         if: ${{ github.event_name != 'workflow_dispatch' }}
         with:
           name: tarballs