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
(cherry picked from commit c353ef04abfe6263c40e7bbc84038eb9ecbf6d70)
Merge "Use Title::getPrefixedText in UpdateRepoOnMoveJob" into mw1.23-wmf6