[DataPipe] Fix MapDataPipe spawn lambda test (#85668)
The test in its original form fails and I believe it is because the expected result is incorrect, unless we expect different behaviors between `IterDataPipe` and `MapDataPipe` in multiprocessing.
Differential Revision: [D39832182](https://our.internmc.facebook.com/intern/diff/D39832182)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85668
Approved by: https://github.com/ejguan
