Add Ruby 3.4 and head into test matrix

Author: voxik

.github/workflows/ruby.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: ['2.5', '3.0', '3.1', '3.2', '3.3']
+        ruby-version: ['2.5', '3.0', '3.1', '3.2', '3.3', '3.4', 'head']
 
     steps:
     - uses: actions/checkout@v4