Update EventFlow.MongoDB to 2.28

[Jaben]

First, thank you for this excellent library -- it's genuinely one of the best. You guys do a great job -- I know how thankless open source can be -- so THANK YOU.

But the latest MongoDB.Driver breaks bindings. I can't compile my solution with EventFlow anymore:

I'll do a PR here today/tomorrow for this update.

[rasmus]

Thanks for reporting and creating the PR ❤️

[rasmus]

Released in 0.84.4