chore(rds): support 8.4.3 engine version for Amazon RDS for MySQL (#3…

…2257)

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

```sh
% 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
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

packages/aws-cdk-lib/aws-rds/lib/instance-engine.ts

@@ -950,6 +950,8 @@ export class MysqlEngineVersion {
   public static readonly VER_8_0_39 = MysqlEngineVersion.of('8.0.39', '8.0');
   /** Version "8.0.40". */
   public static readonly VER_8_0_40 = MysqlEngineVersion.of('8.0.40', '8.0');
+  /** Version "8.4.3". */
+  public static readonly VER_8_4_3 = MysqlEngineVersion.of('8.4.3', '8.0');
 
   /**
    * Create a new MysqlEngineVersion with an arbitrary version.