Unable to use pin D6/PA8 for External Interrupt on Portenta H7

[snapchaturvedi]

Describe the bug
I am using the following simple program based on extint_wakeup.py example to wakeup Portenta from lightsleep but as soon as I run the code it wakes up without any external interruption.

To Reproduce
Run the following program on Portenta H7 with Vision Shield (LoRa):

import time
import pyb
import machine
from pyb import Pin, ExtInt


def callback(line):
    pass


led = pyb.LED(3)
pin = Pin("D6", Pin.IN, Pin.PULL_DOWN)
ext = ExtInt(pin, ExtInt.IRQ_RISING, Pin.PULL_DOWN, callback)

# Enter Stop Mode. Note the IDE will disconnect.
machine.sleep()

while True:
    led.on()
    time.sleep_ms(100)
    led.off()
    time.sleep_ms(100)

Expected behavior
The Portenta should stay in sleep mode until external voltage is provided to pin D6 for it to wake up.

Please complete the following information

• IDE version: 4.2.4
• Firmware version: 4.5.9
• Board: Arduino Portenta + Vision Shield (LoRa)
• OS: Windows

[facchinm]

Let's only keep openmv/openmv#2647 open