add ruby 3 to test matrix

Author: Ben Miller

.github/workflows/ruby.yml

@@ -30,6 +30,8 @@ jobs:
         - '2.5'
         - '2.6'
         - '2.7'
+        - '3.0'
+        - '3.1'
         - jruby-9.1.17.0
         - jruby-9.2.21.0
         - jruby-9.3.6.0