Test with all supported Rails versions in CI

Author: mvz

.github/workflows/ruby.yml

@@ -26,6 +26,13 @@ jobs:
     strategy:
       matrix:
         ruby: ["3.0", "3.1", "3.2", "3.3"]
+        gemfile:
+          - rails_61
+          - rails_70
+          - rails_71
+
+    env:
+      BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}.gemfile
 
     steps:
       - uses: actions/checkout@v4