Add support for sha256 repositories (#23894)

Currently only SHA1 repositories are supported by Gitea. This adds
support for alternate SHA256 with the additional aim of easier support
for additional hash types in the future.

Fixes: #13794
Limited by: https://github.com/go-git/go-git/issues/899
Depend on: #28138

<img width="776" alt="图片" src="https://github.com/go-gitea/gitea/assets/81045/5448c9a7-608e-4341-a149-5dd0069c9447">

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

modules/git/repo_base_gogit.go

@@ -21,6 +21,10 @@ import (
 	"github.com/go-git/go-git/v5/storage/filesystem"
 )
 
+func init() {
+	isGogit = true
+}
+
 // Repository represents a Git repository.
 type Repository struct {
 	Path string