ci: split lint and test jobs, handle conditional rubocop dependency

Author: jsmmr

.github/workflows/build.yml

@@ -1,7 +1,17 @@
 name: build
 on: [push]
 jobs:
-  build:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '4.0'
+          bundler-cache: true
+      - run: bundle exec rubocop
+
+  test:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -20,5 +30,4 @@ jobs:
         run: |
           bundle config path vendor/bundle
           bundle install --jobs 4 --retry 3
-      - run: bundle exec rubocop
       - run: bundle exec rspec

Gemfile

@@ -4,3 +4,8 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in callable_tree.gemspec
 gemspec
+if RUBY_VERSION >= '2.7.0'
+  group :development do
+    gem 'rubocop', '~> 1.69', require: false
+  end
+end

callable_tree.gemspec

@@ -31,7 +31,6 @@ Gem::Specification.new do |spec|
   # spec.add_dependency "example-gem", "~> 1.0"
   spec.add_development_dependency 'rake', '~> 13.3'
   spec.add_development_dependency 'rspec', '~> 3.13'
-  spec.add_development_dependency 'rubocop', '~> 1.69'
 
   # For more information and examples about making a new gem, checkout our
   # guide at: https://bundler.io/guides/creating_gem.html