fixed(ci):Update i18n fetch

Author: Suyunmeng

.github/workflows/i18n_sync.yml

@@ -32,6 +32,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: ${{ vars.SYNC_LANG_ENV_BACKEND_REPOSITORY || 'OpenListTeam/OpenList' }}
+          ref: main
           path: backend
           fetch-depth: 0
           submodules: recursive