Test against Ruby 3.1

Author: composerinteralia

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby_version: ["2.6", "2.7", "3.0"]
+        ruby_version: ["2.6", "2.7", "3.0", "3.1"]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2