Correct backend in pipe_with_ddp_test (#60123)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60123
All of the tests would run with gloo, but some tests specify a
different backend param which we should respect.
ghstack-source-id: 131688188
Test Plan: CI
Reviewed By: cbalioglu
Differential Revision: D29171549
fbshipit-source-id: 3e306060df189c0e38d5ca6dd34f4b4fbca052b9