Add Ruby v4 to test matrix

Author: sshaw

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby: ['3.4', '3.3', '3.2', '3.1', '3.0', '2.7']
+        ruby: ['4', '3.4', '3.3', '3.2', '3.1', '3.0', '2.7']
 
     steps:
       - uses: actions/checkout@v5