[BUGFIX] Consider all relevant pids when populating BE TS constants

The TemplateService - if no TSFE is available - uses the rootline
to find a matching site. Previously it only considered the top most
element of the root line for finding a site, now it also considers
all pages in the rootline with is_siteroot set.

Resolves: #97172
Releases: main, 11.5
Change-Id: I39d2e980b91addbbce40666cada5ee63cb88d6a8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73956


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>