Avoid initializing `new_group` in test_backward_no_ddp. (#40727)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40727
This unit test doesn't need to initialize a PG, as a result avoiding
initializing a process group.
#Closes: https://github.com/pytorch/pytorch/issues/40292
ghstack-source-id: 106817362
Test Plan: waitforbuildbot
Differential Revision: D22295131
fbshipit-source-id: 5a60e91e4beeb61cc204d24c564106d0215090a6
