Bump ruby/setup-ruby from 1.207.0 to 1.208.0

Bumps [ruby/setup-ruby](https://github.com/ruby/setup-ruby) from 1.207.0 to 1.208.0.
- [Release notes](https://github.com/ruby/setup-ruby/releases)
- [Changelog](https://github.com/ruby/setup-ruby/blob/master/release.rb)
- [Commits](ruby/setup-ruby@4a9ddd6...868b3f0)

---
updated-dependencies:
- dependency-name: ruby/setup-ruby
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Update .ruby-version with matrix value
         run: echo "${{ matrix.ruby_version }}" >| .ruby-version
       - name: Set up Ruby
-        uses: ruby/setup-ruby@4a9ddd6f338a97768b8006bf671dfbad383215f4
+        uses: ruby/setup-ruby@868b3f088412f139260f27f5b148179b9dd6b008
         with:
           bundler-cache: true
       - name: Run tests