[USART] Add check for rescheduling in `IRQhandleInterrupt`

After miosix2.7, it seems that checking for a higher thread to schedule after irqwakeup is more than mandatory. If not done, it not only leads to scheduling higher priority threads after the current lower priority one, but can lead to starving/deadlock.

If the only active thread is the IdleThread and another thread is waken up by an interrupt, if the ISR doesn't reschedule the waken up thread it won't be never scheduled: the idle thread will continue executing without checking for threads with higher priority.