Fix build failure

* Change ruby matrtix to test non-EOL ruby versions
* Change GitHub Actions CI workfloat o use actions/upload-artifact@v4
* Upgrade mutant to 0.12.4
* Change mutant config to specify the usage is opensource

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: [2.1, 2.3, 2.4, 2.5, 2.6, 2.7, '3.0', 3.1, 3.2, head, jruby, jruby-head, truffleruby, truffleruby-head]
+        ruby-version: [3.1, 3.2, head, jruby, jruby-head, truffleruby, truffleruby-head]
         os: [ubuntu-latest]
     steps:
     - uses: actions/checkout@v3
@@ -36,7 +36,7 @@ jobs:
           echo 'Mutant not supported on ${{ matrix.ruby-version }}'
         fi
     - name: Upload coverage
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       if: success()
       with:
         name: coverage-${{ matrix.ruby-version }}

Gemfile

@@ -8,13 +8,11 @@ group :test do
   gem 'rspec',     '~> 3.8', '>= 3.8.0'
   gem 'yardstick', '~> 0.9', '>= 0.9.9'
 
-  if RUBY_ENGINE.eql?('ruby') && RUBY_VERSION >= '2.7'
-    gem 'mutant',       '~> 0.11', '>= 0.11.22'
-    gem 'mutant-rspec', '~> 0.11', '>= 0.11.22'
-    gem 'simplecov',    '~> 0.22', '>= 0.22.0'
+  gem 'mutant',       '~> 0.12.4'
+  gem 'mutant-rspec', '~> 0.12.4'
+  gem 'simplecov',    '~> 0.22', '>= 0.22.0'
 
-    source 'https://oss:sxCL1o1navkPi2XnGB5WYBrhpY9iKIPL@gem.mutant.dev' do
-      gem 'mutant-license'
-    end
+  source 'https://oss:sxCL1o1navkPi2XnGB5WYBrhpY9iKIPL@gem.mutant.dev' do
+    gem 'mutant-license'
   end
 end

config/mutant.yml

@@ -1,4 +1,5 @@
 ---
+usage: opensource
 integration:
   name: rspec
 requires:

memoizable.gemspec

@@ -16,5 +16,5 @@ Gem::Specification.new do |gem|
   gem.files            = %w[CONTRIBUTING.md LICENSE.md README.md memoizable.gemspec] + Dir['lib/**/*.rb']
   gem.extra_rdoc_files = Dir['**/*.md']
 
-  gem.required_ruby_version = '>= 2.1'
+  gem.required_ruby_version = '>= 3.1'
 end