Use reusing workflow for Ruby versions

Author: hsbt

.github/workflows/test.yml

@@ -3,11 +3,18 @@ name: build
 on: [push, pull_request]
 
 jobs:
+  ruby-versions:
+    uses: ruby/actions/.github/workflows/ruby_versions.yml@master
+    with:
+      engine: cruby
+      min_version: 2.5
+
   build:
+    needs: ruby-versions
     name: build (${{ matrix.ruby }} / ${{ matrix.os }})
     strategy:
       matrix:
-        ruby: [ 2.7, 2.6, 2.5, head ]
+        ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest, windows-latest ]
         exclude:
           - { os: macos-latest, ruby: '2.5' }