Extract rubocop to a separate job

.github/workflows/ci.yml

@@ -6,7 +6,18 @@ on:
     branches: [master]
 
 jobs:
-  ci:
+  rubocop:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.0
+          bundler-cache: true
+      - name: Run rubocop
+        run: bundle exec rubocop
+  test:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -17,9 +28,6 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby-version }}
-      - name: Install dependencies
-        run: bundle install
-      - name: Run rubocop
-        run: bundle exec rubocop
+          bundler-cache: true
       - name: Run tests
         run: bundle exec rspec