docs(core): correct comment (#34714)

### Description
Just a small comment fix for the `CfnOutput` class :)

### 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: Uaitt

packages/aws-cdk-lib/core/lib/cfn-output.ts

@@ -48,7 +48,7 @@ export class CfnOutput extends CfnElement {
   private _exportName?: string;
 
   /**
-   * Creates an CfnOutput value for this stack.
+   * Creates a CfnOutput value for this stack.
    * @param scope The parent construct.
    * @param props CfnOutput properties.
    */