Use bundle exec to run rubocop.

Author: moroland

.github/workflows/linting.yml

@@ -18,4 +18,4 @@ jobs:
           ruby-version: '3.1'
           bundler-cache: true # runs 'bundle install' and caches installed gems automatically
       - name: Rubocop
-        run: rubocop -f github
+        run: bundle exec rubocop -f github