ci: update Ruby version and refactor (#109)

Signed-off-by: Daijiro Fukuda <[email protected]>

Author: daipom

.github/workflows/unit-test.yml

@@ -10,22 +10,17 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '3.2', '3.1', '3.0', '2.7' ]
+        ruby: [ '3.4', '3.3', '3.2' ]
         os: [ 'ubuntu-latest', 'macOS-latest', 'windows-latest' ]
-        # It should be removed after RubyInstaller 3.2 is available on setup-ruby
-        exclude:
-          - os: windows-latest
-            ruby: 3.2
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: unit testing
       env:
         CI: true
       run: |
-        gem install bundler rake
-        bundle install --jobs 4 --retry 3
         bundle exec rake test