fix: cd 트리거 일시적으로 변경 for 테스트

.github/workflows/cd.yml

@@ -9,7 +9,7 @@ name: backend_cd
 
 on:
   pull_request:
-    types: [ closed ]
+    types: [ opened, reopened, synchronize ]
     branches: [ 'main' ]
 
 jobs:
@@ -22,6 +22,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
       - name: Early exit
         if: ${{ !contains(github.event.pull_request.labels.*.name, '백엔드') }}
         run: |