fix a typo in optimization_tutorial.py #4258

Job	Run time
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	23m 17s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	33m 49s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	24m 47s
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	16m 20s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	20m 23s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	28m 18s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	18m 49s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	16m 22s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	24m 12s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	36m 1s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	26m 33s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	15m 56s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	17m 24s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	28m 31s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	23m 18s
pytorch_tutorial_build_manager	25m 2s
	6h 19m 2s

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