Add Close() method to gogitRepository (#8901) (#8956)

Backport #8901 

In investigating #7947 it has become clear that the storage component of go-git repositories needs closing.

This PR adds this Close function and adds the Close functions as necessary.

In TransferOwnership the ctx.Repo.GitRepo is closed if it is open to help prevent the risk of multiple open files.

Fixes #7947

modules/repofiles/update.go

@@ -429,6 +429,7 @@ func PushUpdate(repo *models.Repository, branch string, opts models.PushUpdateOp
 	if err != nil {
 		return fmt.Errorf("OpenRepository: %v", err)
 	}
+	defer gitRepo.Close()
 
 	if err = repo.UpdateSize(); err != nil {
 		log.Error("Failed to update size for repository: %v", err)