Update CHANGELOG to require minimum Jenkins version

Author: froque

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  - [Test with Java 25 and Java 21](https://github.com/jenkinsci/visual-basic-6-plugin/pull/15)
  - [Automate dependency updates](https://github.com/jenkinsci/visual-basic-6-plugin/pull/17)
  - [Ban JUnit 4 imports](https://github.com/jenkinsci/visual-basic-6-plugin/pull/18)
+ - [Require 2.504.3 as minimum Jenkins version](https://github.com/jenkinsci/visual-basic-6-plugin/pull/19)
 
 ## [v2.3] - 2025-02-17