chore(rds): add MySQL version 5.7.44-rds.20250508 (#34576)

### Reason for this change

A new MySQL enging version `5.7.44-rds.20250508` is available.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Concepts.VersionMgmt.html#MySQL.Concepts.VersionMgmt.Supported

### Description of changes

Added the MySQL engine version `5.7.44-rds.20250508`.

### Describe any new or updated permissions being added

N/A

### Description of how you validated changes

```console
$ aws --region us-east-1 rds describe-db-engine-versions --engine mysql --query 'DBEngineVersions[].EngineVersion'
[
    "5.7.44",
    "5.7.44-rds.20240408",
    "5.7.44-rds.20240529",
    "5.7.44-rds.20240808",
    "5.7.44-rds.20250103",
    "5.7.44-rds.20250213",
    "5.7.44-rds.20250508",
    "8.0.32",
    "8.0.33",
    "8.0.34",
    "8.0.35",
    "8.0.36",
    "8.0.37",
    "8.0.39",
    "8.0.40",
    "8.0.41",
    "8.0.42",
    "8.4.3",
    "8.4.4",
    "8.4.5"
]
```

### 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: Tietew

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

@@ -893,6 +893,8 @@ export class MysqlEngineVersion {
   public static readonly VER_5_7_44_RDS_20250103 = MysqlEngineVersion.of('5.7.44-rds.20250103', '5.7');
   /** Version "5.7.44-rds.20250213". */
   public static readonly VER_5_7_44_RDS_20250213 = MysqlEngineVersion.of('5.7.44-rds.20250213', '5.7');
+  /** Version "5.7.44-rds.20250508". */
+  public static readonly VER_5_7_44_RDS_20250508 = MysqlEngineVersion.of('5.7.44-rds.20250508', '5.7');
 
   /** Version "8.0" (only a major version, without a specific minor version). */
   public static readonly VER_8_0 = MysqlEngineVersion.of('8.0', '8.0');