Actions: Switch ruby/setup-ruby to v1

Per the action's docs (https://github.com/marketplace/actions/setup-ruby-jruby-and-truffleruby#versioning),
they strongly prefer folks reference `v1` instead of a more-specific
version tag or commit ID: "This will provide the best experience by
automatically getting bug fixes, new Ruby versions and new features."

.github/workflows/jekyll.yml

@@ -34,7 +34,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Setup Ruby
-        uses: ruby/setup-ruby@8575951200e472d5f2d95c625da0c7bec8217c42 # v1.161.0
+        uses: ruby/setup-ruby@v1
         with:
           ruby-version: '3.1' # Not needed with a .ruby-version file
           bundler-cache: true # runs 'bundle install' and caches installed gems automatically