SyncBatchNorm.forward() to handle optional weight (#54568)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/54495
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54568
Reviewed By: ezyang
Differential Revision: D27285822
Pulled By: malfet
fbshipit-source-id: 4f7b489d80294cb2509eec4f6c4aa22d5c47b35d
