TYPO3 Core

`SiteBasedTestTrait` created a instance of the `SiteConfiguration`
using the PHP `new` keyword for writing functional test instance
site configurations.

It is possible, that the `SiteConfiguration` is retrieved from
the `Dependency Injection container` by code executed before
the test releated site configuration is written, which does not
reset the instance based `SiteConfiguration->$firstLevelCache`
property and later retrieving site configurations using the
`SiteFinder`, for example in rootline and other operations,
cannot find the test instance configurations.