ci: Use SSH agent and accept host key

ci/Jenkinsfile

@@ -13,7 +13,10 @@ pipeline {
     stages {
         stage('Publish') {
             steps {
-                sh '. ci/publish.sh'
+                sshagent(['jenkins-web']) {
+                    sh "ssh -oStrictHostKeyChecking=no ${PUBLISH_USER}@${PUBLISH_HOST} :"
+                    sh '. ci/publish.sh'
+                }
             }
         }
     }