common/gpio: fix warning on re-export (#29457)

common/gpio.py

@@ -1,3 +1,4 @@
+import os
 from functools import lru_cache
 from typing import Optional, List
 
@@ -26,6 +27,9 @@ def gpio_read(pin: int) -> Optional[bool]:
   return val
 
 def gpio_export(pin: int) -> None:
+  if os.path.isdir(f"/sys/class/gpio/gpio{pin}"):
+    return
+
   try:
     with open("/sys/class/gpio/export", 'w') as f:
       f.write(str(pin))