chore(ci): run linting as separate job

.github/workflows/ruby.yml

@@ -33,4 +33,19 @@ jobs:
         bundler-cache: true # runs 'bundle install' and caches installed gems automatically
 
     - name: Run tests
-      run: bundle exec rake
+      run: bundle exec rake spec
+
+  lint:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+
+    - name: Run linting with RuboCop
+      run: bundle exec rake rubocop