Added 3.3 and 3.2 into CI and removed 2.7 and 2.6 from CI

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     name: build ${{ matrix.ruby }}
     strategy:
       matrix:
-        ruby: [ '3.0', 2.7, 2.6 ]
+        ruby: [ '3.3', '3.2', '3.1', '3.0' ]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2