Use `aws-cdk-lib/assertions` #8855

Job	Run time
Lint & Test	1m 32s
Integrate (express-rest-api)	1m 0s
Integrate (greeter)	56s
Integrate (koa-rest-api)	1m 5s
Integrate (lambda-sqs-worker)	1m 18s
Integrate (lambda-sqs-worker-cdk)	58s
Integrate (oss-npm-package)	54s
Integrate (private-npm-package)	57s
	8m 40s

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