When binary files managed by git-lfs are not hosted by the main source repo (e.g. when using the github mirror), the fall-back repo set up by `lfs_fallback_setup` does fetch the files, but the follow-up call to `git pull` in `work_tree_update` does not check them out. This commit simply adds an extra `git lfs checkout` command there. Pull Request: https://projects.blender.org/blender/blender/pulls/139825