Currently, it is impossible to remove the `skipcaptcha` permission from bots. Even after adding `$wgGroupPermissions['bot']['skipcaptcha'] = false;` to LocalSettings.php, bots still have the `skipcaptcha` permission.
Due to this behavior, it is unable to disable the "bot" user group using `unset( $wgGroupPermissions['bot'] );`, as log as the ConfirmEdit extension is installed.
The only way to remove the "bot" user group from a wiki with ConfirmEdit installed is by editing the `$IP\extensions\ConfirmEdit\extension.json` file and removing code that affects bot rights. Editing this sensitive file is not a preferable way to remove the `skipcaptcha` permission from bots. Also, IINM, this file may be overwritten when upgrading.
Therefore, `$wgGroupPermissions['bot']['skipcaptcha'] = false;` should not be ignored when set on LocalSettings.php.
See also: https://www.mediawiki.org/wiki/Topic:Uaai6d7z94fik8kl
Thanks.