sched_ext: Documentation: Clarify ops.dispatch() role in task lifecycle

sched_ext: Documentation: Clarify ops.dispatch() role in task lifecycle

ops.dispatch() is invoked when a CPU becomes available. This can occur
when a task voluntarily yields the CPU, exhausts its time slice, or is
preempted for other reasons.

If the task is still runnable, refilling its time slice in
ops.dispatch() (either by the BPF scheduler or the sched_ext core)
allows it to continue running without triggering ops.stopping().
However, this behavior is not clearly reflected in the current task
lifecycle diagram.

Update the diagram to better represent this interaction.

Fixes: 9465f44d2df2 ("sched_ext: Documentation: Clarify time slice handling in task lifecycle")
Cc: stable@vger.kernel.org # v6.17+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>