fix(rds): incorrect version definition of MySQL 8.4.3 (#32934)

### Issue # (if applicable)

Closes #32933.

### Reason for this change

The major version definition of MySQL 8.4.3 is incorrect.

### Description of changes

Fixed the major version definition of MySQL 8.4.3.

### Describe any new or updated permissions being added




### Description of how you validated changes



### 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)

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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*

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

@@ -959,7 +959,7 @@ export class MysqlEngineVersion {
   /** 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');
+  public static readonly VER_8_4_3 = MysqlEngineVersion.of('8.4.3', '8.4');
 
   /**
    * Create a new MysqlEngineVersion with an arbitrary version.