Add 3.4 in CI

Author: eregon

.github/workflows/ci.yml

@@ -13,10 +13,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, jruby, truffleruby]
+        ruby: [2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, 3.4, jruby, truffleruby]
         os: [ubuntu]
         include:
-          - ruby: 3.3
+          - ruby: ruby
             os: windows
 
     env: