Spurious calls of task state handler in sequencer

[AlexDontsov2008]

Describe the bug
When I enqueued a single task with sequencer and checked a number of times the task state handler processed Started state, I noticed that it was called for all coroutine threads in case of "old" Sequencer and 2 times for experimental Sequencer.

To Reproduce
Steps to reproduce the behavior:

1. Create a handler with atomic counters and setup it to the configuration
2. Create dispatcher and sequencer with a simple integer key
3. Enqueue a simple task
4. Check counters

Expected behavior
Task state handler must be called only on a thread to which the task is assigned to

Environment (please complete the following information):

• Ubuntu Linux 20.04