Update Jenkinsfile

add git checkout stage

Jenkinsfile

@@ -8,6 +8,17 @@ pipeline {
     agent any
 
     stages {
+        stage('Checkout') {
+            steps {
+                checkout([
+                    $class: 'GitSCM',
+                    branches: [[ name: '*/main' ]],
+                    userRemoteConfigs: [[
+                        url: 'https://github.com/Trance-0/NoteNextra',
+                    ]]
+                ])
+            }
+        }
         stage('Test') {
             steps {
                 nodejs(nodeJSInstallationName: 'NodeJS') {