chore: Git Actions에서 Ubuntu 기본 shell이 bash이기 때문에 설정 코드 제거 #33

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#defaults

Author: PgmJun

.github/workflows/be-cd-dev.yml

@@ -16,7 +16,6 @@ jobs:
 
     defaults:
       run:
-        shell: bash
         working-directory: ./backend
 
     steps: