XWiki's scheduler in subwiki allows scheduling operations for any main wiki user

XWiki Platform is a generic wiki platform. Starting in version 1.2-milestone-2 and prior to versions 15.10.9 and 16.3.0, any user with an account on the main wiki could run scheduling operations on subwikis. To reproduce, as a user on the main wiki without any special right, view the document `Scheduler.WebHome` in a subwiki. Then, click on any operation (*e.g.,* Trigger) on any job. If the operation is successful, then the instance is vulnerable. This has been patched in XWiki 15.10.9 and 16.3.0. As a workaround, those who have subwikis where the Job Scheduler is enabled can edit the objects on `Scheduler.WebPreferences` to match the patch.