Bump actions/download-artifact from 4.1.7 to 4.1.8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4.1.7 to 4.1.8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4.1.7...v4.1.8)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/deploy_bookdown.yml

@@ -81,7 +81,7 @@ jobs:
        uses: actions/checkout@master
 
      - name: Download artifact
-       uses: actions/download-artifact@v4.1.7
+       uses: actions/download-artifact@v4.1.8
        with:
          # Artifact name
          name: _book # optional