I can't find a better way to do this. It's very hard to trigger an
actual failure in the import process these days. For now I've just made
this work with the new assumptions. May be worth removing the test in
the future if this ever backfires.
Contains minor changes to async usage in line with upstream API changes.
I believe a feedback issue we were seeing with offset changes (the only
component using async write flow) may have been resolved by these
upstream changes (see [release
notes](https://github.com/realm/realm-dotnet/releases/tag/10.14.0)) but
am not investigating further just yet.