fix: add ruby/setup-ruby to release-please workflow

bundle install requires Ruby to be available on the runner.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gjtorikian

.github/workflows/release-please.yml

@@ -32,6 +32,12 @@ jobs:
           ref: ${{ fromJSON(steps.release.outputs.pr).headBranchName }}
           token: ${{ steps.generate-token.outputs.token }}
 
+      - name: Set up Ruby
+        if: steps.release.outputs.pr
+        uses: ruby/setup-ruby@c4e5b1316158f92e3d49443a9d58b31d25ac0f8f # v1.306.0
+        with:
+          ruby-version: ruby
+
       - name: Bundle install and commit
         if: steps.release.outputs.pr
         run: |