Use determineLatestNodeRuntime instead of NODEJS_LATEST

[hlascelles]

CDK is being very cautious about making Node 22.x the latest. aws/aws-cdk#34117

Maybe too cautious? 18.x (which is what lambda.Runtime.NODEJS_LATEST returns) is now in maintenance mode.

It appears determineLatestNodeRuntime may do a better job using the latest runtime.

So can we make that change here, if it works?