tests: semaphore: add k_thread_join to test_sem_take_timeout_isr

This adds k_thread_join() to the thread being used in
test_sem_take_timeout_isr() to avoid a thread re-use error
in the test after this one.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

tests/kernel/semaphore/semaphore/src/main.c

@@ -585,6 +585,8 @@ void test_sem_take_timeout_isr(void)
 	k_sem_reset(&simple_sem);
 
 	expect_k_sem_take_nomsg(&simple_sem, SEM_TIMEOUT, 0);
+
+	k_thread_join(&sem_tid_1, K_FOREVER);
 }
 
 /**