tests: Kernel: semaphore: semaphore: Set test case to 1cpu

The test_sem_take_timeout_isr depends on the thread's priority. But for
SMP platforms, the priority is different with no-SMP. High-priority
threads and low-priority threads might run simultaneously at different
cores. Set the test case run at 1cpu to fix such an issue.

Signed-off-by: Jaxson Han <jaxson.han@arm.com>