[BUGFIX] Wrong typehint in TypoScriptFrontendController

The variable $pageCache in TypoScriptFrontendController misses "Core" in
the namespace.

Change-Id: I5f9ee3bf36951194c74627e4e2bc9d17f5c639e5
Fixes: #55448
Reviewed-on: https://review.typo3.org/27141
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters