Add rubocop linting step to CI build

So we don't accidentally introduce violations.

Author: floehopper

.github/workflows/test.yml

@@ -22,12 +22,18 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/${{ matrix.gemfile }}.gemfile
     steps:
     - uses: actions/checkout@v3
+
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby-version }}
         rubygems: 3.4.10
         bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+
+    - name: Run linter
+      if: matrix.ruby-version == '3.3' && matrix.gemfile == 'rails_7.2'
+      run: bundle exec rubocop
+
     - name: Run tests
       run: bundle exec rspec