Add tanh_backward to AT symbols (#70071)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70071
This commit adds tanh_backward to aten_interned_strings.h as an AT symbol.
Test Plan: CI.
Reviewed By: mruberry
Differential Revision: D33173370
Pulled By: alanwaketan
fbshipit-source-id: e20ed2a807156ce772b7c1e3f434fa895116f4c3
