Increase number of iterations in DDP SPMD tests (#40506)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/40506
Test Plan: Imported from OSS
Differential Revision: D22208965
Pulled By: mrshenli
fbshipit-source-id: 7d27b60e2c09e641b4eeb1c89d9f9917c4e72e52
