Sync LFS objects if fetch_result.check_repo_changed

What does this MR do and why?

⚠ This MR needs Introduce new `FetchRemoteResponse.repo_changed... (gitaly#6363 - closed) completed first because we need a new FetchRemoteResponse.repo_changed field which will require a GitLab MR and new version of the gitaly gem.

This MR aims to sync LFS objects before git branch data is updated in order to avoid a race condition that exists where git branch data is updated but LFS objects are still being sync'd.

Related

• Pull Mirroring - Synchronize LFS objects before... (&15147)
• Sync LFS objects if fetch_result.check_repo_cha... (#486867 - closed)
• Introduce new `FetchRemoteResponse.repo_changed... (gitaly#6363 - closed)

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