[FSDP][BE] Change assert to assertEqual (#73787)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/73787
Test Plan: Imported from OSS
Reviewed By: zhaojuanmao
Differential Revision: D34643865
Pulled By: awgu
fbshipit-source-id: 9c0463c5f5b6fce266c5141b3ba2ce029c32f61c
(cherry picked from commit 0cf94934a1f26a4dc7637fb74e02f5a4ef866f7d)
