fix: refs #8715 update condition for changelog stage in Jenkinsfile to use IS_PROTECTED_BRANCH

Jenkinsfile

@@ -77,7 +77,7 @@ pipeline {
         }
         stage('Changelog') {
             when {
-                expression { !PROTECTED_BRANCH }
+                expression { !IS_PROTECTED_BRANCH }
             }
             steps {
                 script {
@@ -85,7 +85,7 @@ pipeline {
                         script: "git fetch origin ${TARGET_BRANCH} && git diff --name-only origin/${TARGET_BRANCH}",
                         returnStdout: true
                     ).trim().split('\n')
-                    echo "DIFF: ${diffOutput}"
+                    echo "DIFF: ${diffOutput}" // diffOutput
                     def hasChangelog = diffOutput.any { it == 'CHANGELOG.md' }
 
                     if (!hasChangelog) {