[TASK] Avoid phpstan warnings LinkButton::setHref() expects string

Resolves: #96760
Releases: main, 11.5
Change-Id: I7007c579fd3677e09229b0941f905dce8014cdfa
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73319


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>