[jenkins-jobs] Run check contributors in correct dir

jenkins-jobs/scripts/release-pipeline.groovy

@@ -259,11 +259,13 @@ node('Slave') {
     }
 
     stage ('Check Contributors') {
+        dir (DEBEZIUM_DIR) {
             def rc = sh(script: "jenkins-jobs/scripts/check-contributors.sh", returnStatus: true)
             if (rc != 0) {
                 error "Error, not all contributors have been added to COPYRIGHT.txt.  See log for details."
             }
         }
+    }
 
     stage ('Check Jira') {
         if (!DRY_RUN) {