Update ruby.yml

Author: wenbinf

.github/workflows/ruby.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['3.4']
+        ruby-version: ['2.6', '2.7', '3.0']
 
     steps:
     - uses: actions/checkout@v4
@@ -29,6 +29,6 @@ jobs:
         ruby-version: ${{ matrix.ruby-version }}
         bundler-cache: true # runs 'bundle install' and caches installed gems automatically
     - name: Setup bundler
-      run: gem install bundler:2.6.6
+      run: gem install bundler:1.17.2
     - name: Run tests
       run: bundle exec rake