Fix test asserted arguments

Author: Avasam

setuptools/tests/test_sandbox.py

@@ -127,7 +127,7 @@ def write_file():
         cmd, args, kwargs = caught.value.args
         assert cmd == 'open'
         assert args == ('/etc/foo', 'w')
-        assert kwargs == {}
+        assert kwargs == {"encoding": locale.getpreferredencoding(False)}
 
         msg = str(caught.value)
         assert 'open' in msg