Don't test against Ruby head

Author: andyw8

.github/workflows/ci.yml

@@ -12,10 +12,8 @@ jobs:
         gemfile:
           - Gemfile
           - gemfiles/Gemfile-rails-main
-        ruby: ["3.0", "3.1", "3.2", "3.3", "head"]
+        ruby: ["3.0", "3.1", "3.2", "3.3"]
         include:
-          - ruby: "head"
-            experimental: true
           - gemfile: "gemfiles/Gemfile-rails-main"
             experimental: true
         exclude: