chore(rds): support 8.4.3 engine version for Amazon RDS for MySQL

[mazyu36]

Add a new minor version.

Ref

• https://aws.amazon.com/about-aws/whats-new/2024/11/amazon-rds-for-mysql-8-4-lts-release/
• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Concepts.VersionMgmt.html#MySQL.Concepts.VersionMgmt.Supported

% aws rds describe-db-engine-versions --engine mysql --query "DBEngineVersions[].EngineVersion" --output table --region us-east-1
--------------------------
|DescribeDBEngineVersions|
+------------------------+
|  5.7.44                |
|  5.7.44-rds.20240408   |
|  5.7.44-rds.20240529   |
|  5.7.44-rds.20240808   |
|  8.0.32                |
|  8.0.33                |
|  8.0.34                |
|  8.0.35                |
|  8.0.36                |
|  8.0.37                |
|  8.0.39                |
|  8.0.40                |
|  8.4.3                 |
+------------------------+

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.17%. Comparing base (74086a0) to head (df084e3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #32257   +/-   ##
=======================================
  Coverage   77.17%   77.17%           
=======================================
  Files         105      105           
  Lines        7169     7169           
  Branches     1315     1315           
=======================================
  Hits         5533     5533           
  Misses       1455     1455           
  Partials      181      181           

Flag	Coverage Δ
suite.unit	77.17% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	77.17% <ø> (ø)

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: df084e3
• Result: SUCCEEDED
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