Add Ruby 3.3 & Rails 8 to CI matrix

Author: tricknotes

.github/workflows/tests.yml

@@ -16,6 +16,8 @@ jobs:
         ruby: ["3.1", "3.2", "3.3"]
         rails: ["6.1", "7.0", "7.1", "7.2"]
         include:
+          - ruby: "3.3"
+            rails: "8.0"
           - ruby: "3.3"
             rails: "main"