Reduce test field size to (2^31 - 1) to support 32 bit systems

Author: Melissa0x1f992

Lib/test/test_ctypes/test_struct_fields.py

@@ -79,7 +79,7 @@ def test_gh126937(self):
         class X(self.cls):
             _fields_ = [('char', c_char),]
         class Y(self.cls):
-            _fields_ = [('largeField', X * (2 ** 32))]
+            _fields_ = [('largeField', X * (2 ** 32 - 1))]
 
     # __set__ and __get__ should raise a TypeError in case their self
     # argument is not a ctype instance.