[TASK] Avoid implicitly nullable class method parameter in `EXT:redirects`

With PHP 8.4 marking method parameter implicitly nullable
is depreacted and will emit a `E_DEPRECATED` warning. One
recommended way to resolve this, is making it explicitly
nullable using the `?` nullable operator. [1]

This prepares the way towards PHP 8.4 compatibility.

[1] https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated

Resolves: #104184
Releases: main, 12.4, 11.5
Change-Id: I1e1a60a36ae2b5244bbd8c3cf963f2165077dbad
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84866


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