Support only Rubies that are supported upstream

Co-authored-by: m-nakamura145 <[email protected]>

Author: 2 people

.github/workflows/ubuntu.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: [ 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2, 3.3, head ]
+        ruby: [ 3.1, 3.2, 3.3, head ]
     steps:
       - uses: actions/checkout@v4
       - name: Setup ruby

gems.gemspec

@@ -17,5 +17,5 @@ Gem::Specification.new do |spec|
   spec.homepage      = 'https://github.com/rubygems/gems'
   spec.licenses      = %w[MIT]
   spec.require_paths = %w[lib]
-  spec.required_ruby_version = '>= 2.1.9'
+  spec.required_ruby_version = '>= 3.1.0'
 end