Fix: add event sync in fsdp tutorial (#3166) #3655

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	11m 22s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	51m 54s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	18m 11s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	31m 52s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	21m 37s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	19m 21s
pytorch_tutorial_build_worker (7, 15, linux.4xlarge.nvidia.gpu)	18m 31s
pytorch_tutorial_build_worker (8, 15, linux.4xlarge.nvidia.gpu)	13m 7s
pytorch_tutorial_build_worker (9, 15, linux.4xlarge.nvidia.gpu)	22m 13s
pytorch_tutorial_build_worker (10, 15, linux.4xlarge.nvidia.gpu)	17m 43s
pytorch_tutorial_build_worker (11, 15, linux.4xlarge.nvidia.gpu)	15m 3s
pytorch_tutorial_build_worker (12, 15, linux.4xlarge.nvidia.gpu)	32m 57s
pytorch_tutorial_build_worker (13, 15, linux.4xlarge.nvidia.gpu)	43m 50s
pytorch_tutorial_build_worker (14, 15, linux.4xlarge.nvidia.gpu)	34m 7s
pytorch_tutorial_build_worker (15, 15, linux.4xlarge.nvidia.gpu)	28m 24s
pytorch_tutorial_build_manager	21m 35s
	6h 41m 47s

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