[AMQ-9235] Update Jenkins JDK 19 -> JDK 20 (#994)

JDK 20 compile succeeds
diff --git a/Jenkinsfile b/Jenkinsfile
index 80db4d5..c1880aa 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -68,12 +68,12 @@
             }
         }
 
-        stage('Build JDK 19') {
+        stage('Build JDK 20') {
             tools {
-                jdk "jdk_19_latest"
+                jdk "jdk_20_latest"
             }
             steps {
-                echo 'Building JDK 19'
+                echo 'Building JDK 20'
                 sh 'java -version'
                 sh 'mvn -version'
                 sh 'mvn -U -B -e clean install -DskipTests'