Add 3.4.0-rc1

Author: soutaro

.github/workflows/ruby.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['3.1', '3.2', '3.3', head]
+        ruby: ['3.1', '3.2', '3.3', '3.4.0-rc1', head]
         rubyopt: [""]
         job:
           - test