Modernise the testing matrix

Author: brendon

.github/workflows/main.yml

@@ -15,16 +15,14 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
-          - '3.0'
-          - '3.1'
           - '3.2'
           - '3.3'
+          - '3.4'
+          - '4.0'
         rails:
-          - '6.1'
-          - '7.0'
-          - '7.1'
           - '7.2'
           - '8.0'
+          - '8.1'
         db:
           - mysql
           - postgresql