docs(apigateway): fix doc of Vary header for allowOrigins (#33519)

### Issue # (if applicable)

### Reason for this change



The doc of `Vary` header for `allowOrigins` seems to be wrong. It will be included if it is not `Cors.ALL_ORIGINS`.

> If Cors.ALL_ORIGINS is specified, the Vary: Origin response header will also be included.

see:

https://github.com/go-to-k/aws-cdk/blob/9154927fa0959238c4ddf9ba807cc912fa05a5e6/packages/aws-cdk-lib/aws-apigateway/lib/resource.ts#L224

### Description of changes



Change to:

> If specific origins are specified (not `Cors.ALL_ORIGINS`), the `Vary: Origin` response header will also be included.

### Describe any new or updated permissions being added




### 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)

----

*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-apigateway/lib/cors.ts

@@ -15,8 +15,8 @@ export interface CorsOptions {
    * `[ * ]`.
    *
    * Responses will include the `Access-Control-Allow-Origin` response header.
-   * If `Cors.ALL_ORIGINS` is specified, the `Vary: Origin` response header will
-   * also be included.
+   * If specific origins are specified (not `Cors.ALL_ORIGINS`), the `Vary: Origin`
+   * response header will also be included.
    *
    * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Origin
    */