Jenkinsfile-GitLab-Container: declare local vars in slave job triggers

Declare `localStatus` and `localResult` as local variables in `triggerSlaveJob`
and `triggerCN5GSlaveJob` functions by adding `def`.

This prevents unintended use of global variables in pipeline and avoids
potential variable leakage or conflicts between stages.

Follows the Jenkins recommendation:
Did you forget the `def` keyword? WorkflowScript seems to be setting a field named localStatus (to a value of type RunWrapper) which could lead to memory leaks or other issues.
Did you forget the `def` keyword? WorkflowScript seems to be setting a field named localResult (to a value of type String) which could lead to memory leaks or other issues.

ci-scripts/Jenkinsfile-GitLab-Container

@@ -864,7 +864,7 @@ def triggerSlaveJob (jobName, gitlabStatusName) {
   // The slave job is triggered with the propagate false so the following commands are executed
   // Its status is now PASS/SUCCESS from a stage pipeline point of view
   // localStatus variable MUST be analyzed to properly assess the status
-  localStatus = build job: jobName,
+  def localStatus = build job: jobName,
     parameters: [
       string(name: 'eNB_Repository', value: String.valueOf(GIT_URL)),
       string(name: 'eNB_Branch', value: String.valueOf(env.gitlabSourceBranch)),
@@ -873,7 +873,7 @@ def triggerSlaveJob (jobName, gitlabStatusName) {
       booleanParam(name: 'eNB_mergeRequest', value: "MERGE".equals(env.gitlabActionType)),
       string(name: 'eNB_TargetBranch', value: String.valueOf(env.gitlabTargetBranch))
     ], propagate: false
-  localResult = localStatus.getResult()
+  def localResult = localStatus.getResult()
   echo "${jobName} Slave Job status is ${localResult}"
   gitlabCommitStatus(name: gitlabStatusName) {
     if (localStatus.resultIsBetterOrEqualTo('SUCCESS')) {
@@ -899,11 +899,11 @@ def triggerCN5GSlaveJob (jobName, gitlabStatusName) {
   // The slave job is triggered with the propagate false so the following commands are executed
   // Its status is now PASS/SUCCESS from a stage pipeline point of view
   // localStatus variable MUST be analyzed to properly assess the status
-  localStatus = build job: jobName,
+  def localStatus = build job: jobName,
     parameters: [
       string(name: 'FULL_RAN_TAG', value: String.valueOf(fullRanTag))
     ], propagate: false
-  localResult = localStatus.getResult()
+  def localResult = localStatus.getResult()
   echo "${jobName} Slave Job status is ${localResult}"
   gitlabCommitStatus(name: gitlabStatusName) {
     if (localStatus.resultIsBetterOrEqualTo('SUCCESS')) {