tests/kernel/sched/schedule_api: Replace delay with Z_SPIN_DELAY()

This macro was introduced for this purpose

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

tests/kernel/sched/schedule_api/src/main.c

@@ -21,9 +21,7 @@ void spin_for_ms(int ms)
 		/* In the posix arch, a busy loop takes no time, so
 		 * let's make it take some
 		 */
-		if (IS_ENABLED(CONFIG_ARCH_POSIX)) {
-			k_busy_wait(50);
-		}
+		Z_SPIN_DELAY(50);
 	}
 }