CI: Introduce ruby_versions.yml to add supported Ruby versions automatically

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

.github/workflows/linux.yml

@@ -1,14 +1,26 @@
 name: Testing on Ubuntu
 on:
-  - push
-  - pull_request
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+  schedule:
+    - cron: '0 0 1 * *'
 jobs:
+  ruby-versions:
+    uses: ruby/actions/.github/workflows/ruby_versions.yml@master
+    with:
+      engine: cruby
+      min_version: 2.7
   build:
+    needs: ruby-versions
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '2.7', '3.0', '3.1', '3.2', '3.3', '3.4' ]
+        ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
+        exclude:
+          - ruby: head
         os:
           - ubuntu-latest
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}