Bump actions/download-artifact from 5 to 6 (#17)

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>

Author: dependabot[bot]

.github/workflows/nightly.yml

@@ -91,7 +91,7 @@ jobs:
           username: ${{ github.repository_owner }}
           password: ${{ github.token }}
 
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           name: snapshot-master
           path: ./docker-ruby/master/${{ matrix.image.variant }}
@@ -150,7 +150,7 @@ jobs:
 
     steps:
       - name: Download digests
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           path: /tmp/digests
           pattern: digests-${{ matrix.variant }}-*
@@ -194,10 +194,10 @@ jobs:
       - uses: actions/checkout@v5
         with:
           submodules: true
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           name: snapshot-master
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           path: outcome
           pattern: outcome-*