Use distinct signal to wait to cancel the submission

[GangWang01]

Fixes #9298

Context

Waiting using Thread.Sleep(500) in the test is unreliable.

Changes Made

Wait until the specified log appears rather than Thread.Sleep(500).

Testing

Notes

[JanKrivanek]

Looks as a good way to get rid of some of the pesky flakyness - great!

I'd love to see the test to not iterate the log events repetitively. We can use MockLogger to avoid the additional thread/task and 'wake-check-sleep' pattern here

[JanKrivanek]

Thank you!