fix document listing unwrap from automation scripting context

Caused by: java.lang.ClassCastException: java.util.ArrayList cannot be cast to org.nuxeo.ecm.automation.core.scripting.DocumentWrapper
    at org.nuxeo.automation.scripting.internals.AutomationMapper.unwrapContext(AutomationMapper.java:94)
    at org.nuxeo.automation.scripting.internals.AutomationMapper.executeOperation(AutomationMapper.java:56)
    at jdk.nashorn.internal.scripts.Script$Recompilation$7$24592AA$\^eval\_.SetNodeVariable(<eval>:589)
    at jdk.

function run(input, params) {

  var wokflowInitiatorVar = ctx.workflowInitiator;

 Workflow.SetNodeVariable(input, {

    'name':'assignee' ,

    'value':  'Administrator'
});

}