chore(doc): INTEGRATION_TESTS (#25299)

As the module has renamed in #25056 the doc should reflect the change accordingly.

Closes #<issue number here>.

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INTEGRATION_TESTS.md

@@ -85,7 +85,7 @@ _integ.lambda.ts_
 import * as iam from '@aws-cdk/aws-iam';
 import * as cdk from '@aws-cdk/core';
 import * as lambda from '../lib';
-import * as integ from '@aws-cdk/integ-tests';
+import * as integ from '@aws-cdk/integ-tests-alpha';
 
 const app = new cdk.App();