main.yml in grumlin-0.15.2

- old
+ new

@@ -20,10 +20,10 @@
           bundle exec rubocop
   test:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ["2.7", "3.0"]
+        ruby: ["2.7", "3.0", "3.1"]
     steps:
       - uses: actions/checkout@v2
 
       - uses: ruby/setup-ruby@v1
         with: