OZG-7906 fix Jenkinsfile duplicate variable name

Jenkinsfile

@@ -50,7 +50,7 @@ pipeline {
                     FAILED_STAGE = env.STAGE_NAME
                     def rootVersion = getPomVersion('pom.xml')
                     def jobVersion = getPomVersion('aggregation-manager-job/pom.xml')
-                    def jobVersion = getPomVersion('aggregation-manager-server/pom.xml')
+                    def serverVersion = getPomVersion('aggregation-manager-server/pom.xml')
 
                     if(rootVersion != jobVersion) {
                         error("Version in aggregation-manager-job stimmt nicht mit dem parent überein.")