feat(rds): support 8.0.40 engine version for RDS for MySQL (#32117)

Support new minor version

* Ref: [Amazon RDS for MySQL supports new minor version 8.0.40
](https://aws.amazon.com/about-aws/whats-new/2024/11/amazon-rds-mysql-new-minor-version/)

### 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*

Author: mazyu36

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

@@ -948,6 +948,8 @@ export class MysqlEngineVersion {
   public static readonly VER_8_0_37 = MysqlEngineVersion.of('8.0.37', '8.0');
   /** Version "8.0.39". */
   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');
 
   /**
    * Create a new MysqlEngineVersion with an arbitrary version.