@raj99918 Please update the script include script as follows.

var Groupsdata= Class.create();
Groupsdata.prototype = Object.extendsObject(global.AbstractAjaxProcessor, {

    getGroupnames: function(user) {
        var groups = [];        
        var gr = new GlideRecord('sys_user_grmember');
        gr.addQuery('user', user);
        gr.query();
        while (gr.next()) {
            groups.push(gr.group.sys_id);
        }
        return 'sys_idIN' + groups.toString();         
    },
type: 'Groupsdata'
});

Also, apply the same reference qualifier again on the Group field in order to make the reference qualifier call the script include.