[TASK] Update typo3fluid/fluid to 2.6.0

Fixes missing output in ifAuthenticatedViewHelper after cache clearing
and erroneous replication of field properties to subsequent fields.

composer command used:
composer update typo3fluid/fluid

Resolves: #86930
Resolves: #86890
Resolves: #87430
Resolves: #86910
Resolves: #87586
Releases: master, 9.5
Change-Id: I8d1abd0aa08d7d7399ec23675dcf07d08dbdd2f2
Reviewed-on: https://review.typo3.org/59554


Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: Jonas Eberle <flightvision@googlemail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>