TEST: Add MySQL CI workflow

.github/workflows/ruby.yml

@@ -10,6 +10,18 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     services:
+      mysql:
+        image: mysql
+        env:
+          MYSQL_ROOT_PASSWORD: root
+          MYSQL_DATABASE: test
+        ports:
+          - 3306:3306
+        options: >-
+          --health-cmd "mysqladmin ping"
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
       postgres:
         image: postgres
         env:
@@ -35,6 +47,7 @@ jobs:
           - 5.2.4.4
           - 5.1.7
         database_url:
+          - mysql2://root:root@127.0.0.1:3306/test
           - postgresql://postgres:password@localhost:5432/test
           - sqlite3:test_db
         exclude:
@@ -59,4 +72,4 @@ jobs:
       - name: Install dependencies
         run: bundle install --jobs 4 --retry 3
       - name: Run tests
-        run: bundle exec rake test
+        run: bundle exec rake test

Gemfile

@@ -10,6 +10,7 @@ version = ENV['RAILS_VERSION'] || 'default'
 
 platforms :ruby do
   gem 'pg'
+  gem 'mysql2'
 
   if version.start_with?('4.2', '5.0')
     gem 'sqlite3', '~> 1.3.13'
@@ -26,4 +27,4 @@ when 'default'
   gem 'railties', '>= 6.0'
 else
   gem 'railties', "~> #{version}"
-end
+end