Fix #31271. When gogit is enabled, `IsObjectExist` calls `repo.gogitRepo.ResolveRevision`, which is not correct. It's for checking references not objects, it could work with commit hash since it's both a valid reference and a commit object, but it doesn't work with blob objects. So it causes #31271 because it reports that all blob objects do not exist.
Git Module
This module is merged from https://github.com/go-gitea/git which is a Go module to access Git through shell commands. Now it's a part of gitea's main repository for easier pull request.