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)

modules/repository/branch.go

@@ -32,7 +32,7 @@ func SyncRepoBranches(ctx context.Context, repoID, doerID int64) (int64, error)
 
 	log.Debug("SyncRepoBranches: in Repo[%d:%s]", repo.ID, repo.FullName())
 
-	gitRepo, err := git.OpenRepository(repo)
+	gitRepo, err := git.OpenRepository(ctx, repo)
 	if err != nil {
 		log.Error("OpenRepository[%s]: %w", repo.FullName(), err)
 		return 0, err

modules/repository/repo.go

@@ -46,7 +46,7 @@ func SyncRepoTags(ctx context.Context, repoID int64) error {
 		return err
 	}
 
-	gitRepo, err := git.OpenRepository(repo)
+	gitRepo, err := git.OpenRepository(ctx, repo)
 	if err != nil {
 		return err
 	}