jenkinsfile: checkout GERRIT_REFSPEC

Change-Id: Id616cc1a53e3d86f220c8bde5a2e0a4c1213f1b6

extras/ci/client-qt-gnulinux/Jenkinsfile

@@ -56,7 +56,7 @@ pipeline {
             steps {
                 script {
                     sh """
-                        git fetch ssh://sblin@review.jami.net:29420/jami-client-qt $GERRIT_REFSPEC && git checkout FETCH_HEAD
+                        git fetch ssh://jenkins@review.jami.net:29420/jami-client-qt $GERRIT_REFSPEC && git checkout FETCH_HEAD
                         git rev-parse HEAD
                         git submodule update --init --recursive
                     """