docs: fix changelog formatting

Author: TheRealAmazonKendra

CHANGELOG.v2.md

@@ -2,7 +2,7 @@
 
 All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
 
-### [2.51.1](https://github.com/aws/aws-cdk/compare/v2.51.0...v2.51.1) (2022-11-18)
+## [2.51.1](https://github.com/aws/aws-cdk/compare/v2.51.0...v2.51.1) (2022-11-18)
 
 
 ### Bug Fixes