Disabling a user account changes its author, allowing RCE from user account in XWiki

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. When an admin disables a user account, the user's profile is executed with the admin's rights. This allows a user to place malicious code in the user profile before getting an admin to disable the user account. To reproduce, as a user without script nor programming rights, edit the about section of your user profile and add `{{groovy}}services.logging.getLogger("attacker").error("Hello from Groovy!"){{/groovy}}`.
As an admin, go to the user profile and click the "Disable this account" button. Then, reload the page. If the logs show `attacker - Hello from Groovy!` then the instance is vulnerable. This has been patched in XWiki 14.10.21, 15.5.5, 15.10.6 and 16.0.0. Users are advised to upgrade. There are no known workarounds for this vulnerability.

### Workarounds
We're not aware of any workaround except upgrading.

### References
* https://jira.xwiki.org/browse/XWIKI-21611
* https://github.com/xwiki/xwiki-platform/commit/f89c8f47fad6e5cc7e68c69a7e0acde07f5eed5a