CI: Use Ruby 3.1+

Centralize Ruby versions list.

.github/workflows/ci.yml

@@ -7,18 +7,20 @@ on:
     branches: [ master ]
 
 jobs:
-  test:
+  ruby-versions:
+    uses: ruby/actions/.github/workflows/ruby_versions.yml@master
+    with:
+      min_version: 3.1
+      engine: cruby
 
+  test:
+    needs: ruby-versions
     runs-on: ubuntu-latest
 
     strategy:
       matrix:
-        ruby-version:
-          - 3.3
-          - 3.2
-          - 3.1
-          - "3.0"
-
+        ruby-version: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
+
     steps:
       - uses: actions/checkout@v4
       - name: Set up Ruby ${{ matrix.ruby-version }}