Add ruby 3.1 and rails 7.0 to ci matrix

Author: Jolyon Pawlyn

.github/workflows/ci.yml

@@ -13,6 +13,8 @@ jobs:
       matrix:
         include:
           # Recent Rubies and Rails
+          - ruby-version: '3.1'
+            rails-version: '7.0'
           - ruby-version: '3.0'
             rails-version: '7.0'
           - ruby-version: '2.7'