chore(lambda): dotnet 9 runtime support (aws#33625)

### Reason for this change
lambda DotNet 9 runtime support.



### Description of changes
[runtimes](https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtimes.html)

### 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-lambda/lib/runtime.ts

@@ -252,6 +252,13 @@ export class Runtime {
     supportsSnapStart: true,
   });
 
+  /**
+   * The .NET 9 runtime (dotnet9)
+   */
+  public static readonly DOTNET_9 = new Runtime('dotnet9', RuntimeFamily.DOTNET_CORE, {
+    supportsSnapStart: true,
+  });
+
   /**
    * The .NET Core 1.0 runtime (dotnetcore1.0)
    * @deprecated Legacy runtime no longer supported by AWS Lambda. Migrate to the latest .NET Core runtime.