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/git/tree_nogogit.go

@@ -26,7 +26,7 @@ func (t *Tree) ListEntries(ctx context.Context, gitRepo *Repository) (Entries, e
 		return t.entries, nil
 	}
 
-	batch, cancel, err := gitRepo.CatFileBatch(ctx)
+	batch, cancel, err := gitRepo.CatFileBatch()
 	if err != nil {
 		return nil, err
 	}