sched/fair: Always trigger resched at the end of a protected period

Always trigger a resched after a protected period even if the entity is
still eligible. It can happen that an entity remains eligible at the end
of the protected period but must let an entity with a shorter slice to run
in order to keep its lag shorter than slice. This is particulalry true
with run to parity which tries to maximize the lag.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-7-vincent.guittot@linaro.org