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_entry_nogogit.go

@@ -18,7 +18,7 @@ func (te *TreeEntry) GetSize(ctx context.Context, gitRepo *Repository) int64 {
 		return te.size
 	}
 
-	batch, cancel, err := gitRepo.CatFileBatch(ctx)
+	batch, cancel, err := gitRepo.CatFileBatch()
 	if err != nil {
 		log.Debug("error whilst reading size for %s in %s. Error: %v", te.ID.String(), gitRepo.LogString(), err)
 		return 0