caos.backends.yaml: Fix a call to CaosQLCursor.prepare()
caos.backends.yaml: Fix a call to CaosQLCursor.prepare()

Fix up another broken call to CaosQLCursor.prepare().  My search/fixup
kung-fu wasn't at it's best when I introduced that proto_schema
argument...

edgedb/edgedb,edgedb/edgedb,edgedb/edgedb