chore(deps): bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/evals-nightly.yml

@@ -53,7 +53,7 @@ jobs:
 
       - name: 'Upload Results'
         if: 'always()'
-        uses: 'actions/upload-artifact@v4' # ratchet:exclude
+        uses: 'actions/upload-artifact@v6' # ratchet:exclude
         with:
           name: 'eval-results-${{ matrix.model }}'
           path: 'eval-results-${{ matrix.model }}.json'