test store: Make TestGlobalStore.doInsertAccount not drop ackedPushToken

Without this line, if a test `globalStore.add`s an account with a
non-null `ackedPushToken`, the field will be null in app code or
test code that retrieves the account from `globalStore`. Thankfully
no tests have been doing that, but it'll be convenient to do that
soon, for testing the unregister-token part of logging out.

test/model/test_store.dart

@@ -111,6 +111,7 @@ class TestGlobalStore extends GlobalStore {
       zulipFeatureLevel: data.zulipFeatureLevel.value,
       zulipVersion: data.zulipVersion.value,
       zulipMergeBase: data.zulipMergeBase.value,
+      ackedPushToken: data.ackedPushToken.value,
     );
   }