.github/workflows/test.yml in prawn-emoji-5.0.0 vs .github/workflows/test.yml in prawn-emoji-5.1.0

@@ -10,19 +10,19 @@
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
     strategy:
       matrix:
         ruby_version:
-          - 2.6
-          - 2.7
-          - 3.0
+          - '2.6'
+          - '2.7'
+          - '3.0'
         prawn_version:
-          - 2.3
-          - 2.4
+          - '2.3'
+          - '2.4'
         exclude:
-          - ruby_version: 3.0
-            prawn_version: 2.3
+          - ruby_version: '3.0'
+            prawn_version: '2.3'
 
     steps:
     - uses: actions/checkout@v2
 
     - uses: hidakatsuya/setup-diff-pdf@v1
@@ -38,6 +38,6 @@
       run: |
         gem install bundler
         bundle install --gemfile gemfiles/prawn-${{ matrix.prawn_version }}.gemfile --jobs 4 --retry 3
 
     - name: Run Tests
-      run: bundle exec rake test
+      run: xvfb-run -a bundle exec rake test