chore: some integ tests fail because two synths have different output (…

…aws#22411)

We added salting of asset hashes to the integ tests, but got the scope wrong: the salt used to be unique per CDK app synth, but some integ tests synth multiple times and compare the outputs.

Make the salt unique per run of the tests instead.

Fixes the pipeline.


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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/test/integ/cli/app/app.js

@@ -371,7 +371,7 @@ class BuiltinLambdaStack extends cdk.Stack {
 
 const app = new cdk.App({
   context: {
-    '@aws-cdk/core:assetHashSalt': `${Date.now()}`, // Force all assets to be unique
+    '@aws-cdk/core:assetHashSalt': process.env.CODEBUILD_BUILD_ID, // Force all assets to be unique, but consistent in one build
   },
 });