Use Title::getPrefixedText in UpdateRepoOnMoveJob

this is what we generally do in Wikibase, so we also
need to do it here to make sure this will work correctly
in all cases.

Bug: 53220
Change-Id: I40583d32523d32a0a69ae06fb83008d181f63af4
Merge "Use Title::getPrefixedText in UpdateRepoOnMoveJob"