jenkinsfile: add missing steps

Change-Id: I0844f54e0f4c4e0785938fa88d1f20bbab9cf757

extras/ci/client-qt-gnulinux/Jenkinsfile

@@ -53,6 +53,7 @@ pipeline {
 
     stages {
         stage('SCM Checkout') {
+            steps {
                 // Wipe workspace and fetch jami-daemon
                 checkout changelog: true, poll: false,
                     scm: [$class: 'GitSCM',
@@ -64,6 +65,7 @@ pipeline {
                         submoduleCfg: [],
                         userRemoteConfigs: [[refspec: '${GERRIT_REFSPEC}', url: 'https://${JAMI_GERRIT_URL}/jami-client-qt']]]
             }
+        }
 
         stage('Init repository') {
             steps {