xxx: try cloning buildroot in groovy

ci/Jenkinsfile

@@ -36,8 +36,27 @@ pipeline {
 
         stage('Prepare') {
             steps {
+                checkout(
+                    poll: false,
+                    scm: scmGit(
+                        branches: [[name: 'refs/tags/2025.05.1']],
+                        browser: gitLab('https://gitlab.com/buildroot.org/buildroot/'),
+                        extensions: [
+                            [
+                                $class: 'RelativeTargetDirectory',
+                                relativeTargetDir: 'buildroot',
+                            ],
+                            cloneOption(
+                                shallow: true,
+                                depth: 1,
+                            ),
+                        ],
+                        userRemoteConfigs: [[
+                            url: 'https://gitlab.com/buildroot.org/buildroot.git',
+                        ]],
+                    )
+                )
                 container('jnlp') {
-                    sh 'if [ ! -d buildroot ]; then git clone https://gitlab.com/buildroot.org/buildroot.git -b 2025.05.x --depth 1; else git -C buildroot pull; fi'
                     sh 'if [ ! -d aimee-os ]; then git clone https://git.pyrocufflink.net/AimeeOS/aimee-os.git --depth 1; else git -C aimee-os pull; fi'
                 }
             }