Bump actions/download-artifact from 4 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/equivalence.yml

@@ -43,14 +43,14 @@ jobs:
           pip install --no-deps .
 
       - name: Download PostgreSQL derived schema
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: psql-derived
 
       - name: Download DuckDB database
         # No path: defaults to the working directory ($GITHUB_WORKSPACE inside
         # the container), placing mimic4.db at $GITHUB_WORKSPACE/mimic4.db.
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: duckdb-db