Bump ruby/setup-ruby from 1.254.0 to 1.268.0 (#360)

Bumps [ruby/setup-ruby](https://github.com/ruby/setup-ruby) from 1.254.0 to 1.268.0.
- [Release notes](https://github.com/ruby/setup-ruby/releases)
- [Changelog](https://github.com/ruby/setup-ruby/blob/master/release.rb)
- [Commits](ruby/setup-ruby@2a7b300...8aeb6ff)

---
updated-dependencies:
- dependency-name: ruby/setup-ruby
  dependency-version: 1.268.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.github/workflows/gh-pages.yml

@@ -138,7 +138,7 @@ jobs:
         with:
           fetch-depth: 0 # need full history to get page last modified times
       - name: Setup Ruby
-        uses: ruby/setup-ruby@2a7b30092b0caf9c046252510f9273b4875f3db9 # v1.254.0
+        uses: ruby/setup-ruby@8aeb6ff8030dd539317f8e1769a044873b56ea71 # v1.268.0
         with:
           ruby-version: '3.1'
           bundler-cache: true # runs 'bundle install' and caches installed gems automatically