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/pull/patch.go

@@ -73,7 +73,7 @@ func checkPullRequestMergeableByTmpRepo(ctx context.Context, pr *issues_model.Pu
 	}
 	defer cancel()
 
-	tmpGitRepo, err := git.OpenRepositoryLocal(prCtx.tmpBasePath)
+	tmpGitRepo, err := git.OpenRepositoryLocal(ctx, prCtx.tmpBasePath)
 	if err != nil {
 		return fmt.Errorf("OpenRepository: %w", err)
 	}