Bump actions/download-artifact from 4 to 7

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 7.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v7)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build.yml

@@ -58,7 +58,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.ref == 'refs/heads/master'
     steps:
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v7
       - run: mv notebooks/environment.yml ./environment.yml
       - run: mv index/* ./
       - run: mv pdf/*/*.pdf ./pdf/