chore: still keep ctx in git.Repository struct for cat-file batch command (#38684)

Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.

If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.

http://localhost:3000/-/admin/monitor/perftrace

* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)

services/repository/fork.go

@@ -170,7 +170,7 @@ func ForkRepository(ctx context.Context, doer, owner *user_model.User, opts Fork
 
 	// 6 - Sync the repository branches and tags
 	var gitRepo *git.Repository
-	gitRepo, err = git.OpenRepository(repo)
+	gitRepo, err = git.OpenRepository(ctx, repo)
 	if err != nil {
 		return nil, fmt.Errorf("OpenRepository: %w", err)
 	}