Add link for jenkins build on 3.9 branch

Author: slawekjaranowski

README.md

@@ -32,7 +32,7 @@ Apache Maven
 
 - [3.9.x](https://github.com/apache/maven/tree/maven-3.9.x): 
 [![Maven Central](https://img.shields.io/maven-central/v/org.apache.maven/apache-maven.svg?label=Maven%20Central&versionPrefix=3.)](https://central.sonatype.com/artifact/org.apache.maven/apache-maven)
-![Jenkins Build](https://img.shields.io/jenkins/build?jobUrl=https%3A%2F%2Fci-maven.apache.org%2Fjob%2FMaven%2Fjob%2Fmaven-box%2Fjob%2Fmaven%2Fjob%2Fmaven-3.9.x%2F)
+[![Jenkins Build](https://img.shields.io/jenkins/build?jobUrl=https%3A%2F%2Fci-maven.apache.org%2Fjob%2FMaven%2Fjob%2Fmaven-box%2Fjob%2Fmaven%2Fjob%2Fmaven-3.9.x%2F)][build-3.9]
 [![Java CI](https://github.com/apache/maven/actions/workflows/maven.yml/badge.svg?branch=maven-3.9.x)][gh-build-3.9]
 
 Apache Maven is a software project management and comprehension tool. Based on