Bump actions/download-artifact from 5 to 6 (#8)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

[skip ci]

Author: dependabot[bot]

.github/workflows/build-reactant-reusable.yml

@@ -222,7 +222,7 @@ jobs:
       - name: Load Julia packages from cache
         id: julia-cache
         uses: julia-actions/cache@v2
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           merge-multiple: true
       - name: Change Reactant commit