[iOS] Add nonVarTypeModeGuard to fix the unit test (#39743)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39743
### Summary
Still need this RAII guard for full JIT
### Test Plan
- CI checks
Test Plan: Imported from OSS
Differential Revision: D21968256
Pulled By: xta0
fbshipit-source-id: 8ea63c699fed4e2a01390232a58f039110391844
