Add Ruby 3.3. to main build

Author: JonRowe

.github/workflows/ci.yml

@@ -37,6 +37,9 @@ jobs:
       matrix:
        include:
          # Edge Rails (?) builds >= 3.1
+         - ruby: 3.3
+           env:
+             RAILS_VERSION: 'main'
          - ruby: 3.2
            env:
              RAILS_VERSION: 'main'