Update ruby versions

Author: nobu

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     name: build (${{ matrix.ruby }} / ${{ matrix.os }})
     strategy:
       matrix:
-        ruby: [ '3.0', 2.7, 2.6, 2.5, head ]
+        ruby: [ '3.1', '3.0', '2.7', '2.6', head ]
         os: [ ubuntu-latest, macos-latest ]
     runs-on: ${{ matrix.os }}
     steps:

etc.gemspec

@@ -35,7 +35,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.extensions    = %w{ext/etc/extconf.rb}
 
-  spec.required_ruby_version = ">= 2.3.0"
+  spec.required_ruby_version = ">= 2.6.0"
 
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"