baseCheckout: Add testing job to help debug polling issues

vars/baseCheckout.groovy

+pipeline {
+    agent {
+        label 'docker'
+    }
+
+    stages {
+        stage("Git Checkout") {
+            steps {
+                checkout(
+                    [
+                        $class: 'GitSCM',
+                        branches: [
+                            [
+                                name: "master"
+                            ]
+                        ],
+                        doGenerateSubmoduleConfigurations: false,
+                        extensions: [
+                            [
+                                $class: 'CloneOption',
+                                depth: 0,
+                                noTags: false,
+                                shallow: true
+                            ]
+                        ],
+                        submoduleCfg: [],
+                        userRemoteConfigs: [
+                            [
+                                url: "https://github.com/moodle/moodle.git"
+                            ]
+                        ]
+                    ]
+                )
+            }
+        }
+    }
+}