chore(ci): bump actions/download-artifact from 2 to 3

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 2 to 3.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v2...v3)

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

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

.github/workflows/book.yml

@@ -51,7 +51,7 @@ jobs:
     needs: book
     if: github.event_name == 'push'
     steps:
-    - uses: actions/download-artifact@v2
+    - uses: actions/download-artifact@v3
       with:
         name: book
     - uses: peaceiris/actions-gh-pages@v3