Add empty repo check in DetectAndHandleSchedules (#29606)

![image](https://github.com/go-gitea/gitea/assets/18380374/e6081301-bd3e-4cf6-ba4e-e574348dffb4)

Author: yp05327

services/actions/notifier_helper.go

@@ -486,6 +486,10 @@ func handleSchedules(
 
 // DetectAndHandleSchedules detects the schedule workflows on the default branch and create schedule tasks
 func DetectAndHandleSchedules(ctx context.Context, repo *repo_model.Repository) error {
+	if repo.IsEmpty {
+		return nil
+	}
+
 	gitRepo, err := gitrepo.OpenRepository(context.Background(), repo)
 	if err != nil {
 		return fmt.Errorf("git.OpenRepository: %w", err)