Relax the atol/rtol of layernorm math kernel test. (#49507)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49507
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D25598424
Pulled By: ailzhang
fbshipit-source-id: b3f43e84f177cf7c14831b0b83a399b155c813c4
