(contributing): Build failures don't always include `!!!!!!!!`

### Describe the bug

When a PR CodeBuild build fails, the end of the build text says:

> ❌ Last command failed. Scroll up to see errors in log (search for '!!!!!!!!').

Unfortunately, not all failures have that string. That being present seems to be specific to JSII failures?

### Expected Behavior

The error should be on a line that has `!!!!!!!!` or be pretty obvious/recent in the build output. The message saying how to find a failure should help lead a user to the failure.

### Current Behavior

Due to the parallel nature of the build, the error was way earlier without a `!!!!!!!!` and mixed in with other "random" output:

```
> @aws-cdk/aws-s3objectlambda-alpha:test

aws-cdk-lib: FAIL aws-cloudfront/test/key-value-store.test.ts
aws-cdk-lib: ● Key Value Store › imported resource throws error when missing ID
aws-cdk-lib: expect(received).toThrow(expected)
aws-cdk-lib: Expected pattern: /Invalid Key Store Arn:/
aws-cdk-lib: Received message: "Invalid Key Value Store ID 'arn:aws:cloudfront::123456789012:key-value-store'"
aws-cdk-lib:   169 | const storeId = Arn.split(keyValueStoreArn, ArnFormat.SLASH_RESOURCE_NAME).resourceName;
aws-cdk-lib:   170 | if (!storeId) {
aws-cdk-lib: > 171 | throw new Error(`Invalid Key Value Store ID '${keyValueStoreArn}'`);
aws-cdk-lib:   | ^
aws-cdk-lib:   172 | }
aws-cdk-lib:   173 | return new class Import extends Resource implements IKeyValueStore {
aws-cdk-lib:   174 | readonly keyValueStoreArn: string = keyValueStoreArn;
aws-cdk-lib: at Function.fromKeyValueStoreArn (aws-cloudfront/lib/key-value-store.ts:171:13)
aws-cdk-lib: at aws-cloudfront/test/key-value-store.test.ts:108:27
aws-cdk-lib: at Object. (../../node_modules/expect/build/toThrowMatchers.js:74:11)
aws-cdk-lib: at Object.throwingMatcher [as toThrow] (../../node_modules/expect/build/index.js:320:21)
aws-cdk-lib: at Object. (aws-cloudfront/test/key-value-store.test.ts:109:7)
aws-cdk-lib: at Object. (aws-cloudfront/test/key-value-store.test.ts:109:7)
aws-cdk-lib: PASS aws-ssm/test/util.test.ts
@aws-cdk/aws-route53resolver-alpha: Build times for @aws-cdk/aws-route53resolver-alpha: Total time (53.4s) | /codebuild/output/src2064263468/src/github.com/aws/aws-cdk/tools/@aws-cdk/cdk-build-tools/node_modules/jsii/bin/jsii (41.8s) | /codebuild/output/src2064263468/src/github.com/aws/aws-cdk/node_modules/eslint/bin/eslint.js (10.4s) | /codebuild/output/src2064263468/src/github.com/aws/aws-cdk/tools/@aws-cdk/cdk-build-tools/bin/cdk-awslint (0.9s) | '/usr/bin/node' (0.2s) | pkglint (0.2s)
@aws-cdk/aws-route53resolver-alpha: @aws-cdk/aws-route53resolver-alpha: Done in 53.57s.
```

### Reproduction Steps

1. Review the logs at https://2cl995f30a.execute-api.us-east-1.amazonaws.com/Prod/buildlogs?key=85595289-c0ad-4b14-a403-b343cd25387c%2Fbuild.log
2. See that the actual failure is a unit test failure; that does not have `!!!!!!!!`.

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

N/A

### Framework Version

_No response_

### Node.js Version

N/A

### OS

N/A

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_

Start by reviewing the linked CodeBuild log and the PR build-failure reporting flow. Compare the unit-test failure in aws-cloudfront/test/key-value-store.test.ts with failures that include `!!!!!!!!`; done means the final message reliably directs users to the actual recent failure, even when that marker is absent.

Written by the indexing model from the issue text.