Your flutter checkout has local changes that would be erased by upgrading.

flutter 升级提示

Your flutter checkout has local changes that would be erased by upgrading. If you want to keep these changes, it is recommended that you stash them via “git stash” or else commit the changes to a local branch. If it is okay to remove local changes, then re-run this command with –force.

你的 Flutter 检出目录存在本地修改，升级操作会清除这些修改。如果你想保留这些变更，建议通过 “git stash” 命令暂存修改，或者将变更提交到本地分支。如果可以移除本地修改，请使用 –force 参数重新运行此命令。

就是你在升级Flutter的过程中它检测出你本地的文件有过修改，如果想要保留这些变更则需要你自己暂存一下，如果不需要了则在命令后面加上–force再次运行就可以了