[DOCS] Fix CSRF code example and naming in Changelogs

Adjust request token header name to match the value defined in
RequestToken::HEADER_NAME.

Fix code example.

Releases: main, 12.4
Resolves: #104167
Change-Id: I8e78c0385962b8bdc085a6cc2896794930a96238
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84813


Tested-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>