Add Ruby 3.3 to testing matrix (#150)

.github/workflows/test.yml

@@ -33,7 +33,7 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
-        ruby: ['2.7', '3.0', '3.1', '3.2']
+        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3']
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout