Provide config when constructing WikiImporter in RepoHooksTest

Constructing WikiImporter without Config was depercated in 1.25 and caused
RepoHooksTest to fail.

Change-Id: Idfadf462d9e4cfdfe7213cdc46161cfc300d2261
(cherry picked from commit e5b869325aaf937d3d5b28fb666fc5bd4bac2fa5)