fix(lambda): add @deprecated tag to python3.8 (#32162)

### Issue # (if applicable)

Closes #<issue number here>.

### Reason for this change

Updated according to [this document](https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtimes.html#runtimes-deprecated).

### Description of changes



### 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*

Author: kdnakt

packages/aws-cdk-lib/aws-lambda/lib/runtime.ts

@@ -152,6 +152,7 @@ export class Runtime {
 
   /**
    * The Python 3.8 runtime (python3.8)
+   * @deprecated Legacy runtime no longer supported by AWS Lambda. Migrate to the latest Python runtime.
    */
   public static readonly PYTHON_3_8 = new Runtime('python3.8', RuntimeFamily.PYTHON, {
     supportsInlineCode: true,