Use reusable GitHub Actions

This saves on duplication.

Right now the command must be overridden since the default does not
pass --parallel --format github.

.github/workflows/ruby_ci.yaml

@@ -4,23 +4,18 @@ on:
   push:
     branches:
       - master
+concurrency:
+  group: ${{ github.head_ref }}
+  cancel-in-progress: true
 env:
   RAILS_ENV: test
   DATABASE_URL: postgresql://postgres:@localhost/test
   DATABASE_CLEANER_ALLOW_REMOTE_DATABASE_URL: true
 jobs:
   rubocop:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Setup Ruby
-        uses: ruby/setup-ruby@v1
-        with:
-          ruby-version: 2.7
-          bundler-cache: true
-      - name: Run rubocop
-        if: github.event_name != 'push'
-        run: bundle exec rubocop --parallel --format github
+    uses: theforeman/actions/.github/workflows/rubocop.yml@v0
+    with:
+      command: bundle exec rubocop --parallel --format github
   test_ruby:
     runs-on: ubuntu-latest
     needs: rubocop