Use sys.platform rather than the platform module

Found in issue on mypy: python/mypy#8547 (comment)

j5/boards/board.py

@@ -3,8 +3,8 @@
 import atexit
 import logging
 import os
-import platform
 import signal
+import sys
 from abc import ABCMeta, abstractmethod
 from types import FrameType
 from typing import TYPE_CHECKING, Dict, Optional, Set, Type, TypeVar
@@ -115,7 +115,7 @@ def new_signal_handler(signal_type: signal.Signals, frame: FrameType) -> None:
         terminal_signals = [signal.SIGINT, signal.SIGTERM]
 
         # Add SIGHUP on systems that support it
-        if platform.system() != "Windows":
+        if sys.platform != "win32":
             terminal_signals.append(signal.SIGHUP)
 
         for signal_type in terminal_signals: