Bump shared cache key for test.wikidata (memcached storage of items, etc.)

to go with reverting the Wikidata extension version back to mw1.24-wmf19

Change-Id: I509d236e2c203c977916411e0c26763d3f9e9e04
Merge "Bump shared cache key for test.wikidata (memcached storage of items, etc.)"