fix(crossRegionReference): error message missing stack information

[andreialecu]

Issue #29699

Closes #29699

Reason for this change

The logic was incorrectly using Object.entries() on a Map.

Description of changes

This is a straighforward change to properly handle the map, and an update to tests.

Description of how you validated changes

Updated test

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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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

[aws-cdk-automation]

The pull request linter has failed. See the aws-cdk-automation comment below for failure reasons. If you believe this pull request should receive an exemption, please comment and provide a justification.

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[andreialecu]

Exemption Request - no need, there's a test covering this.

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 251d4b5
• Result: SUCCEEDED
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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

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