Fix Psalm issue

[sebastian-meyer]

Currently Psalm reports the following issue on master:

Error: src/phpDocumentor/Descriptor/Traits/ImplementsInterfaces.php:52:56: LessSpecificImplementedReturnType: The inherited return type 'phpDocumentor\Descriptor\Collection<phpDocumentor\Descriptor\Interfaces\InterfaceInterface|phpDocumentor\Reflection\Fqsen>' for phpDocumentor\Descriptor\Interfaces\ClassInterface::getInterfacesIncludingInherited is more specific than the implemented return type for phpDocumentor\Descriptor\Traits\ImplementsInterfaces::getinterfacesincludinginherited 'phpDocumentor\Descriptor\Collection' (see https://psalm.dev/166)

This PR should fix this by declaring a more specific return type for this method.

[jaapio]

Thanks!