fix: let ruby/setup-ruby auto-detect bundler version from Gemfile.lock

- Removed hardcoded bundler version
- setup-ruby will read BUNDLED WITH from Gemfile.lock automatically
- This keeps bundler version in sync with Gemfile.lock

Author: Goldziher

.github/workflows/ci-ruby.yaml

@@ -145,7 +145,6 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: "3.2"
-          bundler: "4.0.3"
           bundler-cache: false
           working-directory: packages/ruby
 
@@ -545,7 +544,6 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: "3.2"
-          bundler: "4.0.3"
           bundler-cache: false
           working-directory: packages/ruby