CI: Add Ruby 4.0 (#670)

Author: Watson1978

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 20
     strategy:
       matrix:
-        ruby-version: ['3.4']
+        ruby-version: ['4.0']
         imagemagick-version:
           - { full: 7.1.2-10, major-minor: '7.1' }
     name: Lint (Ruby ${{ matrix.ruby-version }}, ImageMagick ${{ matrix.imagemagick-version.major-minor }})
@@ -49,7 +49,7 @@ jobs:
     timeout-minutes: 20
     strategy:
       matrix:
-        ruby-version: ['3.4']
+        ruby-version: ['4.0']
         imagemagick-version:
           - { full: 7.1.2-10, major-minor: '7.1' }
     name: Check RBS (Ruby ${{ matrix.ruby-version }}, ImageMagick ${{ matrix.imagemagick-version.major-minor }})
@@ -85,7 +85,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0.0-preview2']
+        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0']
         imagemagick-version:
           - { full: 7.1.2-10, major-minor: '7.1' }
     name: Ruby ${{ matrix.ruby-version }}

Gemfile

@@ -12,6 +12,7 @@ unless defined? JRUBY_VERSION
   gem 'rubocop-rake', '~> 0.6'
 end
 
+gem 'minitest', '~> 5.0'
 gem 'minitest-reporters'
 gem 'rake'
 gem 'simplecov'