[DDP] Generalize activation checkpoint tests (#74130)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74130
enable these tests to run for all dist backends not just nccl.
ghstack-source-id: 151429410
Test Plan: CI
Reviewed By: awgu
Differential Revision: D34281684
fbshipit-source-id: 956c1b0cafe0502b593dd42b157d518e89a47d8e
(cherry picked from commit 15d58b88362c49565123823f24ca122d5344acc9)
