Fix grammar in reducer warning (#52835)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52835
Addresses comment in https://github.com/pytorch/pytorch/pull/52385
that was missed before landing the PR
ghstack-source-id: 122543534
Test Plan: CI
Reviewed By: SciPioneer
Differential Revision: D26660764
fbshipit-source-id: 3edfebed56f382c1414ba9eb65a753ced7e34154
