Fix: add event sync in fsdp tutorial #3652

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	14m 20s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	52m 20s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	20m 35s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	30m 14s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	21m 57s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	19m 25s
pytorch_tutorial_build_worker (7, 15, linux.4xlarge.nvidia.gpu)	21m 40s
pytorch_tutorial_build_worker (8, 15, linux.4xlarge.nvidia.gpu)	15m 58s
pytorch_tutorial_build_worker (9, 15, linux.4xlarge.nvidia.gpu)	22m 16s
pytorch_tutorial_build_worker (10, 15, linux.4xlarge.nvidia.gpu)	17m 35s
pytorch_tutorial_build_worker (11, 15, linux.4xlarge.nvidia.gpu)	17m 37s
pytorch_tutorial_build_worker (12, 15, linux.4xlarge.nvidia.gpu)	33m 3s
pytorch_tutorial_build_worker (13, 15, linux.4xlarge.nvidia.gpu)	44m 17s
pytorch_tutorial_build_worker (14, 15, linux.4xlarge.nvidia.gpu)	35m 55s
pytorch_tutorial_build_worker (15, 15, linux.4xlarge.nvidia.gpu)	29m 20s
pytorch_tutorial_build_manager	21m 49s
	6h 58m 21s

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