send email on master node

Former-commit-id: 07518d892cb27efe82ac4d181594a31a67795e79

ci/main_jenkinsfile

@@ -234,10 +234,12 @@ spec:
     post {
         always {
             script {
+                node('master') {
                     def notify = load "${env.WORKSPACE}/ci/jenkinsfile/notify.groovy"
                     notify.notify()
                 }
             }
+        }
         success {
             script {
                 updateGitlabCommitStatus name: 'CI/CD', state: 'success'