Updating notebooks using Git pull changes owner to root

If you use git pull to update the notebooks the changed files get the owner and group root:root. This makes the notebook unable to be saved. I tried correcting this locally(docker) by using the $chown --preserve[=ATTR_LIST] but that did not seem to work for some reason.

首先检查仓库的 Dockerfiles 和 notebook 更新工作流，然后在 Docker 环境中重现一次 git pull。追踪更新后的文件为何会归 root:root 所有，并确定允许保存 notebook 的预期所有权。完成标准是更新后的文件仍由 notebook 用户以可写方式拥有。

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