Fix iCloud CalDAV synchronization errors

The proposed changes fix two issues:

1. A typo in the name of a variable referenced inside an if (change in file davitemslistjob.cpp. I believe the original author intended to reference resourcetypeElement, not responseElement. This error does not seem to affect functionality, but I found it while reading code and addressed it.

2. An error in the usage of the calendar-multiget retrieval. As documented in https://datatracker.ietf.org/doc/html/rfc4791#section-7.9 , ics files inside the request are referenced via their relative path. The change introduced corrects this behaviour. This is what was preventing kdav from working with iCloud.