.github: adding ruby versions 3.3 and 3.4

Author: mrjbq7

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        ruby: ['3.1', '3.2']
+        ruby: ['3.1', '3.2', '3.3', '3.4']
 
     runs-on: ${{ matrix.os }}
     name: Ruby ${{ matrix.ruby }} on ${{ matrix.os }}