[TASK] Use correct external link RST syntax

Resolves: #100190
Related: #99499
Releases: main
Change-Id: I1148d368a1f961a34311a0d931999eedbbb0317e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78141


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>