Support Ruby 4 (#422)

* Update to ruby_4_0 in flake

* `ruby -e 'puts RUBY_VERSION' > .ruby-version`

* Update to Ruby 4 in related code

* Update ruby requirements in README

Author: kachick

.github/workflows/ci-ruby.yml

@@ -33,7 +33,7 @@ jobs:
       matrix:
         os: [ubuntu-24.04]
         # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
-        ruby: ['head', '3.4', '3.3']
+        ruby: ['head', '4.0', '3.4']
         gemfile: ['Gemfile', 'gemfiles/oldest/Gemfile']
     runs-on: ${{ matrix.os }}
     env: # $BUNDLE_GEMFILE must be set at the job level, so it is set for all steps

.rubocop.yml

@@ -2,7 +2,7 @@ plugins:
   - rubocop-rake
 
 AllCops:
-  TargetRubyVersion: 3.3
+  TargetRubyVersion: 3.4
   DisplayCopNames: true
   DisabledByDefault: true
   Exclude:

.ruby-version

@@ -1 +1 @@
-3.4.8
+4.0.0

README.md

@@ -7,8 +7,7 @@ Use power_assert inspection in irb
 
 ## Usage
 
-Tested only in ruby-head and the last 2 stable versions\
-So require Ruby 3.3 or higher
+Requires Ruby 4.0, 3.4, or newer.
 
 ```console
 $ gem install irb-power_assert

flake.nix

@@ -28,7 +28,7 @@
               nixfmt-rfc-style
               nixd
 
-              ruby_3_4
+              ruby_4_0
               # Required to build psych via irb dependency
               # https://github.com/kachick/irb-power_assert/issues/116
               # https://github.com/ruby/irb/pull/648

irb-power_assert.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency 'irb', '>= 1.14.0', '< 2.0'
   gem.add_dependency 'power_assert', '>= 2.0.3', '< 4.0'
 
-  gem.required_ruby_version = '>= 3.3'
+  gem.required_ruby_version = '>= 3.4'
 
   # common