Make Java 21 the primary JVM to execute the maven build

Java 21 is the next LTS and projects are allowed to use Java 21 in this
release, therefore it should become the new primary Java version used to
execute the build.

This also will allow us to catch any possible issues with Java 21 used
as build VM.

.github/workflows/mavenBuild.yml

@@ -56,10 +56,12 @@ jobs:
           8
           11
           17
+          21
         mvn-toolchain-id: |
           JavaSE-1.8
           JavaSE-11
           JavaSE-17
+          JavaSE-21
         distribution: 'temurin'
         cache: maven
     - name: Set up Maven

Jenkinsfile

@@ -10,7 +10,7 @@ pipeline {
 	}
 	tools {
 		maven 'apache-maven-latest'
-		jdk 'temurin-jdk17-latest'
+		jdk 'temurin-jdk21-latest'
 	}
 	stages {
 		stage('initialize PGP') {