Add Ruby 3.4 to CI. (#5)

Author: simi

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby-version: ['3.1', '3.2', '3.3', 'head']
+        ruby-version: ['3.1', '3.2', '3.3', '3.4', 'head']
     continue-on-error: ${{ matrix.ruby-version == 'head' }}
 
     steps: