Fix flaky shared flow subscription

[murfel]

#4488

[dkhalanskyjb]

The change makes sense, thanks! However, the failing tests are important. This changes the behavior of other operators non-trivially, and we need to evaluate how big the change is. Could you please classify the tests into those that fail reasonably and those that should ideally still pass? Then, we'll figure out if we need to isolate the change to just collectLatest and will have an idea of how big the impact of the change is.