tests: Move boto3 tests under toxgen #3356

Job	Run time
Flags (pinned) (3.8, ubuntu-22.04)	2m 15s
Flags (pinned) (3.13, ubuntu-22.04)	4m 7s
Flags (pinned) (3.12, ubuntu-22.04)	3m 27s
Flags (pinned) (3.7, ubuntu-22.04)	1m 36s
Flags (pinned) (3.9, ubuntu-22.04)	1m 39s
All pinned Flags tests passed	8s
	13m 12s

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