[FX] Make FX stability warning reference beta (#50394)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50394
Test Plan: Imported from OSS
Reviewed By: Chillee
Differential Revision: D25874188
Pulled By: jamesr66a
fbshipit-source-id: 4fc4e72fec1f3fab770d870fe78cd4ad0f1d6888
