chore: Bump version to 3.8.0 for release #660

Job	Run time
collab-check	3s
wait-for-approval	2s
detect-changes	8s
codestyle-doc-tests (sagemaker-serve)	5m 46s
codestyle-doc-tests (sagemaker-train)	4m 43s
unit-tests (sagemaker-mlops)	37m 8s
unit-tests (sagemaker-core)	1h 6m 17s
unit-tests (sagemaker-serve)	47m 16s
unit-tests (sagemaker-train)	22m 30s
integ-tests (sagemaker-serve)	33m 8s
codestyle-doc-tests (sagemaker-mlops)	7m 25s
integ-tests (sagemaker-train)	42m 23s
codestyle-doc-tests (sagemaker-core)	20m 13s
integ-tests (sagemaker-core)	34m 8s
integ-tests (sagemaker-mlops)	36m 41s
	5h 57m 51s

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