chore(rds): add postgres engine 16.8, 15.12, 14.17 and 13.20

[phuhung273]

Issue # (if applicable)

None

Reason for this change

https://aws.amazon.com/about-aws/whats-new/2025/04/amazon-aurora-postgresql-versions/

Description of how you validated changes

$ aws rds describe-db-engine-versions --engine postgres --output table --query 'DBEngineVersions[*].{Engine:Engine,EngineVersion:EngineVersion}'
|  postgres |  13.20               |
|  postgres |  14.12               |
|  postgres |  14.13               |
|  postgres |  14.15               |
|  postgres |  14.17               |
|  postgres |  15.7                |
|  postgres |  15.8                |
|  postgres |  15.10               |
|  postgres |  15.12               |
|  postgres |  16.3                |
|  postgres |  16.4                |
|  postgres |  16.6                |
|  postgres |  16.8                |

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

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

[aws-cdk-automation]

(This review is outdated)

[phuhung273]

Exemption Request: Can be verified through CLI

[phuhung273]

Thanks @mazyu36 again for your prompt support 💯

[shikha372]

@Mergifyio update

[mergify]

update

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

[mergify]

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[mergify]

This pull request has been removed from the queue for the following reason: pull request branch update failed.

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[phuhung273]

@Mergifyio update

[mergify]

update

❌ Mergify doesn't have permission to update

For security reasons, Mergify can't update this pull request. Try updating locally.
GitHub response: refusing to allow a GitHub App to create or update workflow .github/workflows/github-merit-badger.yml without workflows permission

Pull request has been modified.

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 87b899a
• Result: SUCCEEDED
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[phuhung273]

You should update or rebase your pull request manually. If you do, this pull request will automatically be requeued once the queue conditions match again.

Oh god, i updated the branch as the bot suggested and ended up dismissing your approval @shikha372 😞 hope you can help reviewing the PR again...