bug(이태겸): dev branch does not appear in the forked repository

## ISSUE
- Group: client
- Type: bug
- Detail: Fork한 이후 Original Repository(codestates)에 branch 추가시
Fork한 Repository에는 추가한 branch가 나오지 않는다

Fork한 Repository에 dev branch가 나오지 않는 이슈는

git remote add upstream https://github.com/codestates/beb-03-YoonSea
git fetch upstream
git merge upstream/dev
[upstream 관련 자료](https://chanhuiseok.github.io/posts/git-2/)

Original Repository(codestates)의 dev branch 에 있는 commit을
제 Local Repository로 가져오는 식으로 진행했습니다

[저의 원격 저장소](https://github.com/royalbluee/beb-03-YoonSea)은 여전히 main branch만 나옵니다

Start by comparing the branches visible in the original repository, the fork, and the local clone, then review the documented upstream commands in the issue. Done means the cause of the missing dev branch is identified and the fork shows the expected branch after the documented workflow.

Written by the indexing model from the issue text.