tests: skip arch_nop test for ARM platforms
tests: skip arch_nop test for ARM platforms

ARM does not guarantee the timing effects of NOP
instruction. Hence skip the test_nop test.
Fix for Issue#42666

Signed-off-by: Mahesh Mahadevan <7f315ec3481825d543f8bec256ad86a4adc9dd8a@nxp.com>

finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr