[BUGFIX] Fix duration determination in Notification.showMessage()

The determination of the duration used in Notification.showMessage() now
takes `SeverityEnum.error` into account and sets the duration to 0,
which is the same behavior when using `Notification.error()`.

Resolves: #97315
Releases: main, 11.5
Change-Id: I1d6f50cc81c8a92031a570eae4e0bffc2b5441a7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74214


Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>