[DOCS] Show correct redirect mode in EXT:felogin documentation

config.typolinkLinkAccessRestrictedPages_addParams works only with
redirectMode getpost.

Releases: main, 11.5, 10.4
Resolves: #97370
Change-Id: I43fc29558eb1d282b4f5939fa115f5350cbede38
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74940


Tested-by: Lina Wolf <112@linawolf.de>
Reviewed-by: Lina Wolf <112@linawolf.de>