[DOCS] Update outdated information about FlashMessagesViewHelper caching

The ViewHelper does not clear cache since 7.3.0 change:
https://review.typo3.org/c/Packages/TYPO3.CMS/+/34818
Still the documentation states it will clear cache.

Instead users need to take care to properly clear cache.
The background:

FlashMessages often tend to be part of a process and already work with
proper cHash and URLs. Unique URLs often lead to unique output of
FlashMessages.
Under some circumstances flash messages might be created before
redirecting to a generic URL.

Resolves: #93636
Releases: master, 10.4
Change-Id: I15479d31671a04ce12336583767277f0fc25cbca
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68173
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/fluid/Classes/ViewHelpers/FlashMessagesViewHelper.php

@@ -116,10 +116,13 @@ public function initializeArguments()
 
     /**
      * Renders FlashMessages and flushes the FlashMessage queue
-     * Note: This disables the current page cache in order to prevent FlashMessage output
-     * from being cached.
      *
-     * @see \TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController::no_cache
+     * Note: This does not disable the current page cache in order to prevent FlashMessage output
+     *       from being cached.
+     *       In case of conditional flash message rendering, caching must be disabled
+     *       (e.g. for a controller action).
+     *       Custom caching using the Caching Framework can be used in this case.
+     *
      * @param array $arguments
      * @param \Closure $renderChildrenClosure
      * @param RenderingContextInterface $renderingContext