runTask: Variable assignment must happen in a script

vars/runTask.groovy

@@ -50,13 +50,15 @@ def call(String task, String branch, String repo, String phpversion, String data
 
             stage("Detect Moodle Version") {
                 steps {
-                    moodleversion = sh (
-                        script: 'grep "\$branch" moodle/version.php | sed "s/^[^\']*\'\\([^\']*\\).*\$/\\1/"',
-                        returnStdout: true
-                    ).trim()
-                    runner = "${env.PATHTORUNNER}/${moodleversion}"
-                    if (!fileExists(runner)) {
-                        runner  "${env.PATHTORUNNER}/master"
+                    script {
+                        moodleversion = sh (
+                            script: 'grep "\$branch" moodle/version.php | sed "s/^[^\']*\'\\([^\']*\\).*\$/\\1/"',
+                            returnStdout: true
+                        ).trim()
+                        runner = "${env.PATHTORUNNER}/${moodleversion}"
+                        if (!fileExists(runner)) {
+                            runner  "${env.PATHTORUNNER}/master"
+                        }
                     }
                 }
             }