Bump actions/upload-artifact from 4 to 6 (#709)

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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/test.yml

@@ -77,7 +77,7 @@ jobs:
         run: echo "SANITIZED_GEMFILE=${{ matrix.gemfile }}" | tr '/' '-' >> $GITHUB_ENV
 
       - name: Upload test coverage folder for later reporting
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ matrix.os }}-${{ matrix.ruby }}-${{ env.SANITIZED_GEMFILE }}
           path: coverage/*.json