Infra: CI 빌드 환경 추가

- 운영환경에 맞춰 CI 환경 MySQL 서비스 추가

Author: namgigun

.github/workflows/backend-ci.yml

@@ -18,6 +18,20 @@ jobs:
         ports:
           - 6379:6379
 
+      mysql:
+        if: github.base_ref == 'main'
+        image: mysql:8
+        ports:
+          - 3306:3306
+        env:
+          MYSQL_ROOT_PASSWORD: root
+          MYSQL_DATABASE: testdb
+        options: >-
+          --health-cmd="mysqladmin ping -h localhost -p$MYSQL_ROOT_PASSWORD"
+          --health-interval=10s
+          --health-timeout=5s
+          --health-retries=3
+
     steps:
       # 저장소 체크아웃
       - name: Checkout repository