"Google Drive can corrupt repositories" in Github Desktop
We've put that warning in place because we've seen quite a few users get their repositories corrupted by various cloud-backed storage solutions such as Google Drive and Dropbox.
The problem boils down to a race condition where Git creates and modifies files rapidly and the storage solution trying to keep up. In some scenarios this can lead to file IO not behaving as Git expects. A storage solution might also erroneously restore a file that was meant to be removed. While these sort of issues are most likely to occur when you're sharing the repository with other people we've seen issues with people who only use the storage for backup purposes.
The best way to backup Git repositories is to commit early and often and push your changes to GitHub frequently, even if you push them to work-in-progress branches rather than master or other long-running branches.
If you're not using GitHub or any other remote and your repository is local I'd recommend creating a bare repository inside your Google Drive and then clone your repository to a location outside of Google Drive and work from there. Whenever you've made changes you can push those to the bare repository. That way you'll have two copies of all your data in case the Google Drive version gets corrupted.