Scope third_party_wikis by category

This issue was created from this discussion.

!82616 (merged) merges contains a data migration to change the category of the third party integrations to "third_party_wiki".

In the milestone after !82616 (merged) merges, the third_party_wikis scope in app/models/integration.rb should be changed to select third party wikis by category: 'third_party_wiki'.