fix(ci): test among ruby HEAD

Author: ProGM

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, '3.0', 3.1, 3.2, 3.3, 3.4, truffleruby-head]
+        ruby: [2.7, '3.0', 3.1, 3.2, 3.3, 3.4, head, truffleruby-head]
 
     steps:
     - uses: actions/checkout@v3