[BUGFIX] Use default page id for fetching a site in SlugService

The rebuildSlugsForSlugChange function of SlugService updates
slugs of sub pages and also creates redirects for them, after
changing the slug of their parent page. This process requires
to fetch the corresponding site configuration.

In cases like changing the slug of a localized root page
this throws a SiteNotFoundException, because the site is
always mapped to the default page id which can not be
determined for localized root pages because their pid is 0.

It's therefore necessary to always use the default page
id for fetching the site through SiteFinder.

Resolves: #92733
Releases: master, 10.4
Change-Id: I8b41647d63d444982b2d2d6f209dea4278034488
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66353


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>