fix(ci): typo on the remote host variables

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

ci-scripts/Jenkinsfile-GitLab-Docker

@@ -204,7 +204,7 @@ pipeline {
                 myShCmd('docker image ls >> archives/amf_docker_image_build.log', rem_u18_host_flag, rem_u18_host_user, rem_u18_host)
                 // We will keep also the TMP image in U18 case.
                 if ("MERGE".equals(env.gitlabActionType)) {
-                  myShCmd('docker image tag oai-amf:' + amf_tag + ' oai-amf:' + rhel_amf_tag, rem_rhel_host_flag, rem_rhel_host_user, rem_rhel_host)
+                  myShCmd('docker image tag oai-amf:' + amf_tag + ' oai-amf:' + rhel_amf_tag, rem_u18_host_flag, rem_u18_host_user, rem_u18_host)
                 }
               }
             }