[pytorch] use correct warning type for tracer warnings (#53460)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53460
We have code to ignore this category of warnings and found this one is incorrect.
Use `stacklevel=2`, otherwise the warning is always filtered by TracerWarning.ignore_lib_warnings()
Test Plan: sandcastle
Reviewed By: wanchaol
Differential Revision: D26867290
fbshipit-source-id: cda1bc74a28d5965d52387d5ea2c4dcd1a2b1e86
