ci: drop Ruby 2.7, add 3.3

.github/workflows/rspec_docker.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ["2.7", "3.0", "3.1", "3.2"]
+        ruby: ["3.0", "3.1", "3.2", "3.3"]
 
     steps:
     - uses: actions/checkout@v4