Bump ruby/setup-ruby from 1.319.0 to 1.321.0

Bumps [ruby/setup-ruby](https://github.com/ruby/setup-ruby) from 1.319.0 to 1.321.0.
- [Release notes](https://github.com/ruby/setup-ruby/releases)
- [Changelog](https://github.com/ruby/setup-ruby/blob/master/release.rb)
- [Commits](ruby/setup-ruby@003a5c4...95ef2b0)

---
updated-dependencies:
- dependency-name: ruby/setup-ruby
  dependency-version: 1.321.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
         with:
           fetch-depth: 0
       - name: Set up Ruby
-        uses: ruby/setup-ruby@003a5c4d8d6321bd302e38f6f0ec593f77f06600 # v1.319.0
+        uses: ruby/setup-ruby@95ef2b042f9d7a56d8268cba8559e2842e2ad01b # v1.321.0
         with:
           bundler-cache: true
       - name: Check RBIs and index