Modify subscription tests not to rely on "onSuccess"

In our subscription hooks, specifically in the internal hook `useSubscription`, we use the `setQueryCache` method to update data.

In our tests we are waiting for `onSuccess` to be called, which [no longer happens.](https://tanstack.com/query/v4/docs/guides/migrating-to-react-query-4#onsuccess-is-no-longer-called-from-setquerydata)

The suggestion in the tanstack docs is to have a useEffect hook depending on the data. I'm not sure how this will look in tests. Will have to investigate.