CI against Ruby 3.3 (#229)

This PR adds Ruby 3.3 to the CI matrix to confirm this gem works with
Ruby 3.3.

Co-authored-by: Elliot Winkler <[email protected]>

Author: y-yagi

.github/workflows/super_diff.yml

@@ -53,6 +53,7 @@ jobs:
           - "3.0"
           - "3.1"
           - "3.2"
+          - "3.3"
         rails_appraisal:
           - rails_6_1
           - rails_7_0