ci: add rubocop workflow

.github/workflows/rubocop.yml

@@ -0,0 +1,22 @@
+name: lint
+
+on:
+  push:
+    branches:
+      - main
+      - dev*
+  pull_request:
+
+jobs:
+  rubocop:
+    runs-on: ubuntu-latest
+    name: RuboCop
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby 3.2
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.2
+          bundler-cache: true
+      - name: Run RuboCop
+        run: bundle exec rubocop

Rakefile

@@ -9,10 +9,6 @@ Rake::TestTask.new(:test) do |t|
   t.test_files = FileList['test/**/test_*.rb']
 end
 
-require 'rubocop/rake_task'
-
-RuboCop::RakeTask.new
-
 require 'rake/extensiontask'
 
 task build: :compile # rubocop:disable Rake/Desc
@@ -27,4 +23,4 @@ Rake::ExtensionTask.new('tiny_linalg') do |ext|
   ext.lib_dir = 'lib/numo/tiny_linalg'
 end
 
-task default: %i[clobber compile test rubocop]
+task default: %i[clobber compile test]