sched/proxy: Yield the donor task

sched/proxy: Yield the donor task

When executing a task in proxy context, handle yields as if they were
requested by the donor task. This matches the traditional PI semantics
of yield() as well.

This avoids scenario like proxy task yielding, pick next task selecting the
same previous blocked donor, running the proxy task again, etc.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202510211205.1e0f5223-lkp@intel.com
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fernand Sieber <sieberf@amazon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251106104022.195157-1-sieberf@amazon.com