fix: use string concat for npm auth to avoid Jenkins sandbox GString.getBytes restriction

Jenkinsfile

@@ -68,7 +68,7 @@ pipeline {
             steps {
                 withCredentials([usernamePassword(credentialsId: 'NEXUS_CREDS', passwordVariable: 'NPM_PASS', usernameVariable: 'NPM_USER')]) {
                     script {
-                        def auth = "${NPM_USER}:${NPM_PASS}".bytes.encodeBase64().toString()
+                        def auth = (NPM_USER + ':' + NPM_PASS).bytes.encodeBase64().toString()
                         writeFile file: '.npmrc', text: "//nexus.xuqinmin.com/repository/npm-hosted/:_auth=${auth}\n"
                         bat "npm publish --registry %NEXUS_REGISTRY%"
                     }