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](https://github.com/actions/upload-artifact/compare/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>

.github/workflows/ci.yml

@@ -75,7 +75,7 @@ jobs:
           bin/bundle exec rspec --exclude-pattern spec/system/local/**/*_spec.rb
 
       - name: Upload coverage report
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: always()
         with:
           name: coverage-report
@@ -83,7 +83,7 @@ jobs:
           if-no-files-found: ignore
 
       - name: Keep screenshots from failed system tests
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: screenshots