Allow adding new files to an empty repo (#24164)

![image](https://user-images.githubusercontent.com/2114189/232561612-2bfcfd0a-fc04-47ba-965f-5d0bcea46c54.png)

modules/git/repo.go

@@ -80,7 +80,7 @@ func InitRepository(ctx context.Context, repoPath string, bare bool) error {
 // IsEmpty Check if repository is empty.
 func (repo *Repository) IsEmpty() (bool, error) {
 	var errbuf, output strings.Builder
-	if err := NewCommand(repo.Ctx, "show-ref", "--head", "^HEAD$").
+	if err := NewCommand(repo.Ctx).AddOptionFormat("--git-dir=%s", repo.Path).AddArguments("show-ref", "--head", "^HEAD$").
 		Run(&RunOpts{
 			Dir:    repo.Path,
 			Stdout: &output,