test: detect OS consistently using platform.system()

test/functional/wallet_multiwallet.py

@@ -9,9 +9,9 @@ Verify that a bitcoind node can load multiple wallet files
 from decimal import Decimal
 from threading import Thread
 import os
+import platform
 import shutil
 import stat
-import sys
 import time
 
 from test_framework.authproxy import JSONRPCException
@@ -143,7 +143,7 @@ class MultiWalletTest(BitcoinTestFramework):
 
         # should raise rpc error if wallet path can't be created
         err_code = -4 if self.options.descriptors else -1
-        assert_raises_rpc_error(err_code, "filesystem error:" if sys.platform != 'win32' else "create_directories:", self.nodes[0].createwallet, "w8/bad")
+        assert_raises_rpc_error(err_code, "filesystem error:" if platform.system() != 'Windows' else "create_directories:", self.nodes[0].createwallet, "w8/bad")
 
         # check that all requested wallets were created
         self.stop_node(0)