ZBXNEXT-5288 added the new functionality to test items. According to its spec:

Only requests from admins and super admins are accepted.

Proposed Fix:
The issue is caused by the zbx_trapper_item_test function:

        if (SUCCEED != zbx_json_value_by_name(jp, ZBX_PROTO_TAG_SID, sessionid, sizeof(sessionid), NULL) ||
                        SUCCEED != DBget_user_by_active_session(sessionid, &user) || USER_TYPE_SUPER_ADMIN > user.type)

USER_TYPE_SUPER_ADMIN here should be replaced with USER_TYPE_ZABBIX_ADMIN