aws-rds: add RDS MySQL engine version 8.4.11

### Describe the feature

Expose RDS for MySQL 8.4.11 as a built-in `MysqlEngineVersion` constant. Amazon RDS for MySQL announced support for this minor version on August 24, 2026.

### Use Case

CDK users should be able to select the newly supported engine version through the same discoverable, strongly typed API used for earlier MySQL 8.4 releases, rather than constructing the version manually.

### Proposed Solution

Add `MysqlEngineVersion.VER_8_4_11` using `MysqlEngineVersion.of('8.4.11', '8.4')`.

Implementation is available in #38735.

### Other Information

- AWS announcement: [Amazon RDS for MySQL now supports new minor version 8.4.11](https://aws.amazon.com/about-aws/whats-new/2026/08/amazon-rds-mysql-8411-available/)
- The current latest built-in MySQL 8.4 constant is `VER_8_4_10`.

### Acknowledgements

- [x] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS CDK Library version (aws-cdk-lib)

Current `main` branch as of September 1, 2026.

### AWS CDK CLI version

N/A — API constant request.

### Environment details (OS name and version, etc.)

N/A — API constant request.

Check issue #38735 first, since the implementation is reported there. If this issue remains unaddressed, locate the MysqlEngineVersion definition and the existing VER_8_4_10 constant, then follow the surrounding version declarations and validation. Done means MySQL 8.4.11 is exposed through the same typed API.

Written by the indexing model from the issue text.