Update tested Ruby versions to 3.1-3.4

Author: pat

.github/workflows/main.yml

@@ -10,9 +10,10 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
-          - 2.7.5
-          - 3.0.3
-          - 3.1.0
+          - '3.1'
+          - '3.2'
+          - '3.3'
+          - '3.4'
 
     steps:
     - uses: actions/checkout@v2