Update Dockerfile to use test-sandbox image for Python 3.12 #2

Job	Run time
Test (3.12)	37s
deploy / Setup	5s
deploy / deploy-staging / build-aws / Build (staging)	2m 12s
deploy / deploy-staging / build-gcp	0s
deploy / deploy-staging / deploy-gcp-staging	0s
deploy / deploy-staging / deploy-staging-aws / Deploy (staging)	9s
deploy / Await Manual Approval (Tests Failed)	0s
deploy / Run Staging Validation Tests	0s
deploy / deploy-production	0s
	3m 3s

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