[BUGFIX] Use correct return type annotations in validation results

Three methods in Extbase's Result are now
annotated with the correct return type to
make PHPStan happy when they are accessed
in custom extensions.

Resolves: #95730
Releases: master, 10.4
Change-Id: I68e4b9a434c9d64037521d45e5c5d0dbcb678094
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71936


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>