UPSTREAM: sched/fair: Fix entity's lag with run to parity

When an entity is enqueued without preempting current, we must ensure
that the slice protection is updated to take into account the slice
duration of the newly enqueued task so that its lag will not exceed
its slice (+ tick).

Bug: 438500731
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-6-vincent.guittot@linaro.org


(cherry picked from commit 3a0baa8e)
Signed-off-by: Qais Yousef <qyousef@google.com>
Change-Id: I9816229f5290bdb054dda8cef4697edba989e5fc