Refactor GitHub Actions workflow to streamline Ruby version matrix

Author: ydah

.github/workflows/main.yml

@@ -1,21 +1,21 @@
 name: Ruby
-
 on:
   push:
     branches:
       - main
-
   pull_request:
-
 jobs:
   build:
     runs-on: ubuntu-latest
     name: Ruby ${{ matrix.ruby }}
     strategy:
       matrix:
         ruby:
-          - '4.0.0'
-
+          - '3.2'
+          - '3.3'
+          - '3.4'
+          - '4.0'
+          - 'head'
     steps:
       - uses: actions/checkout@v4
         with: