[BUGFIX] Use correct type in PageRepository::getDomainStartPage for column fe_group

Strict DBMS will throw an exception for a query where to compare an integer against a column with string values.
There will no "magic" type casting processed, thus we have to use a string instead of an integer.

Change-Id: I740d1797c92f203e83ddfec2ab00df42cc5c53aa
Resolves: #79131
Releases: master
Reviewed-on: https://review.typo3.org/51096


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>