ci: add ruby 3.2 and 3.3 to test matrix

Author: bskim45

.github/workflows/rubygems.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.6', '2.7', '3.0', '3.1']
+        ruby-version: ['2.6', '2.7', '3.0', '3.1', '3.2', '3.3']
 
     steps:
       - uses: actions/checkout@v4